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SHEPARD MISSION
SCIENCE REPORT
REPORT I / LEG 1
4 JANUARY, 3303
PREFACE:
The S.H.E.P.A.R.D Mission of interstellar discovery is named in honor of Alan Shepard, the second human to enter space, and one of only twelve humans to land on the moon during the historic Apollo Missions. Our mission is to obtain scientific data - to observe, document, and collect three primary types of deep space measurements. There are 5 Legs of the SHEPARD Mission. At the completion of each Leg a report will be filed outlining the given scientific findings during each respective Leg. This report, Issue 1, covers Leg-1 of the SHEPARD Mission.
LEG 1 [ORION SPUR & SURROUNDS]:
Leg 1 of the Shepard Mission is a local detailed scan of observable galactic anomalies. It is the aim of Leg 1 of the mission to gather precise data obtainable through detailed surface scans of nearby nebula and star systems. Leg 1 will feature accumulation of data on extremely large red-giant stars, nebulae clusters around Barnard’s Loop, and exhaustive examination of two crucial deep blue planetary nebula. At the end of Leg 1, the crew will perform the first of three Deep-Image-Scans of the galactic core.
GIANTS & STAR CLASSIFICATIONS
Leg-1 of the SHEPARD Mission included detailed scans of many Giant Stars, including the famous Betelgeuse, Rigel, and VY Canis Majoris. This leg, however, also included the discovery of over 20 additional giants hitherto undiscovered. During this process, we learned the basic mechanics of star classification regarding spectra and luminosity - and also discovered two inconsistencies regarding Blue-Supergiants.
STELLAR CLASSIFICATION
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with absorption lines. Each line indicates an ion of a certain chemical element, with the line strength indicating the abundance of that ion. The relative abundance of the different ions varies with the temperature of the photosphere. The spectral class of a star is a short code summarizing the ionization state, giving an objective measure of the photosphere’s temperature and density.
Most stars are currently classified under the Morgan–Keenan (MK) system using the letters O, B, A, F, G, K, and M, a sequence from the hottest (O type) to the coolest (M type). Each letter class is then subdivided using a numeric digit with 0 being hottest and 9 being coolest (e.g. A8, A9, F0, F1 form a sequence from hotter to cooler). The sequence has been expanded with classes for other stars and star-like objects that do not fit in the classical system, such as class D for white dwarfs and class C for carbon stars.
In the MK system, a luminosity class is added to the spectral class using Roman numerals. This is based on the width of certain absorption lines in the star’s spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs. Luminosity class 0 or Ia+ stars for hypergiants, class I stars for supergiants, class II for bright giants, class III for regular giants, class IV for sub-giants, class V for main-sequence stars, class sd for sub-dwarfs, and class D for white dwarfs.
The full spectral class for the Sun is then G2V, indicating a main-sequence star with a temperature around 5,800 K and average luminosity ‘V’.
Following Morgan-Keenan, there are often further sub-classifications regarding luminosity, represented by the letters A&B. A number of different luminosity classes are distinguished for all stellar classes as follows:
0 or Ia+ (hypergiants or extremely luminous supergiants).
Ia (luminous supergiants).
Iab (intermediate luminous supergiants)
Ib (less luminous supergiants)
*While Supergiants are used for example, this division using A&B for luminosity occurs with all luminosity classes from I-VII.
The pilots of SHEPARD have encountered two anomalies with the galactic naming of supergiants on board ships’ computer galactic maps.
1. A giant star is a star with substantially larger radius and luminosity than a main-sequence (or dwarf) star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsprung–Russell diagram and correspond to luminosity classes II and III. The terms giant and dwarf were coined for stars of quite different luminosity despite similar temperature or spectral type by Ejnar Hertzsprung about 1905. Giant stars have radii up to a few hundred times the Sun and luminosities between 10 and a few thousand times that of the Sun. Stars still more luminous than giants are referred to as supergiants and hypergiants.
Stars designated as Blue-White [A / B / O] do not follow the same naming standard in the ship’s computer galmap, insofar as class III Giants are not listed as ‘Giants’. While White & Blue class III giants are rare [often not depicted on many Hertzsprung–Russell diagrams], they still satisfy the criteria of a Giant Star. The galmap correctly identifies K & M class III as giants [orange and red respectively], however counts A, B, & O III giants and IV subgaints as normal stars.
2. B-Class Supergiants [Class I & II] are mislabeled as A-Class Supergiants. This error occurs both in the galactic map screen as well as during FSD initiation when the nav-com reports the destination system. Looking at the detailed information about the given star, however, will indicate that the star is actually a B-Class. Cmdrs are encouraged to inspect both systems to ensure star-classification is correct.
OPEN CLUSTERS & 2MASS STARS
Perhaps the most prominent Open Cluster of stars in the galaxy was the first waypoint of SHEPARD - The Orion Nebula [others include NGC 7822]. Because the Orion Nebula is adjacent to the inhabited bubble, the pilots of SHEPARD have set out to discover new stellar clusters in an attempt to understand more about how they are formed, what ties them together, and what type of stars are most commonly distributed. Finding other open clusters may help us know more about our neighbor the Orion Nebula cluster.
OPEN CLUSTERS
During Leg-1 Cmdr Parabolus located an relatively unexplored open stellar cluster of F-Class stars well below the galactic plane. The cluster was made of roughly 70% F-Class stars and 30% B-Class. The F-Class stars were all designated with the prefix 2MASS, indicating that they were first discovered during the 2MASS observation of the late 20th century [see page 11]. This strange ‘stellar pillar,’ as Parabolus described it, was located in the Sagittarius Gap. Parabolus has since named it the Aether Cluster, after the Greek God Aether. Aether in ancient Greece was one of the primordial deities. Aether is the personification of the upper air. He embodies the pure upper air that the gods breathe, as opposed to the normal air breathed by mortals.
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist. They are loosely bound by mutual gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the galactic center. This can result in a migration to the main body of the galaxy and a loss of cluster members through internal close encounters. Open clusters generally survive for a few hundred million years, with the most massive ones surviving for a few billion years. In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, and can survive for longer. Open clusters have been found only in spiral and irregular galaxies, in which active star formation is occurring.
Young open clusters may not be contained within the molecular cloud from which they formed. Over time, radiation pressure from the cluster will disperse the molecular cloud. Typically, about 10% of the mass of a gas cloud will coalesce into stars before radiation pressure drives the rest of the gas away.
Open clusters are key objects in the study of stellar evolution. Because the cluster members are of similar age and chemical composition, their properties [such as distance, age, metallicity and extinction] are more easily determined than they are for isolated stars. A number of open clusters, such as the Pleiades, Hyades or the Alpha Persei Cluster are visible with the naked eye. Some others, such as the Double Cluster, are barely perceptible without instruments.
The formation of an open cluster begins with the collapse of part of a giant molecular cloud, a cold dense cloud of gas and dust containing up to many thousands of times the mass of the Sun. These clouds have densities that vary from 102 to 106 molecules of neutral hydrogen per cm3, with star formation occurring in regions with densities above 104 molecules per cm3. Typically, only 1–10% of the cloud by volume is above the latter density. Prior to collapse, these clouds maintain their mechanical equilibrium through magnetic fields, turbulence, and rotation.
Many factors may disrupt the equilibrium of a giant molecular cloud, triggering a collapse and initiating the burst of star formation that can result in an open cluster. These include shock waves from a nearby supernova, collisions with other clouds, or gravitational interactions. Even without external triggers, regions of the cloud can reach conditions where they become unstable against collapse. The collapsing cloud region will undergo hierarchical fragmentation into ever smaller clumps, including a particularly dense form known as infrared dark clouds, eventually leading to the formation of up to several thousand stars. This star formation begins enshrouded in the collapsing cloud, blocking the protostars from sight but allowing infrared observation. In the Milky Way galaxy, the formation rate of open clusters is estimated to be one every few thousand years.
It is common for two or more separate open clusters to form out of the same molecular cloud. In the Large Magellanic Cloud, both Hodge 301 and R136 are forming from the gases of the Tarantula Nebula, while in our own galaxy, tracing back the motion through space of the Hyades and Praesepe, two prominent nearby open clusters, suggests that they formed in the same cloud about 600 million years ago. Sometimes, two clusters born at the same time will form a binary cluster. The best known example in the Milky Way is the Double Cluster of NGC 869 and NGC 884 but at least 10 more double clusters are known to exist. Many more are known in the Small and Large Magellanic Clouds—they are easier to detect in external systems than in our own galaxy because projection effects can cause unrelated clusters within the Milky Way to appear close to each other.
There are over 1,000 known open clusters in our galaxy, but the true total may be up to ten times higher than that. In spiral galaxies, open clusters are largely found in the spiral arms where gas densities are highest and so most star formation occurs, and clusters usually disperse before they have had time to travel beyond their spiral arm. Open clusters are strongly concentrated close to the galactic plane. The Aether Open Cluster that Parabolus located is an anomaly - insofar as it was well below the galactic plane and not located within a spiral arm, but rather in the less dense void between them.
The center of the Aether Cluster featured a large class B Star - with an M-Class star orbiting it. What is curious about this stellar pillar is that it is location in Sagittarius Gap - a void between arms. While at first thought one might assume that there might be some sort of invisible gravitational anomaly present in the region - causing these stars to cluster up together, we believe they were actually created in this formation - an echo of a former pulsar nebula whose glowing gases have since blown away - leaving only these relatively dim F class stars amidst five large B-Class brethren. At some point there may have been a super-massive stellar explosion at this location in the very distant past.
Parabolus’ discovery got the pilots of SHEPARD interested in the clustering phenomenon, in the hope that we may understand more about their formation in relation to nebulae. We hope to locate more undiscovered clusters further along in our journey.
STELLAR COMPOSITION AND FATE OF OPEN CLUSTERS
Because open clusters tend to be dispersed before most of their stars reach the end of their lives, the light from them tends to be dominated by the young, hot blue stars. These stars are the most massive, and have the shortest lives of a few tens of millions of years. The older open clusters tend to contain more yellow stars. When a Hertzsprung-Russell diagram is plotted for an open cluster, most stars lie on the main sequence. The most massive stars have begun to evolve away from the main sequence and are becoming red giants; the position of the turn-off from the main sequence can be used to estimate the age of the cluster.
Because the stars in an open cluster are all at roughly the same distance from Earth, and were born at roughly the same time from the same raw material, the differences in apparent brightness among cluster members is due only to their mass. This makes open clusters very useful in the study of stellar evolution, because when comparing one star to another, many of the variable parameters are fixed.
Some open clusters contain hot blue stars which seem to be much younger than the rest of the cluster. These blue stragglers are also observed in globular clusters, and in the very dense cores of globulars they are believed to arise when stars collide, forming a much hotter, more massive star. However, the stellar density in open clusters is much lower than that in globular clusters, and stellar collisions cannot explain the numbers of blue stragglers observed. Instead, it is thought that most of them probably originate when dynamical interactions with other stars cause a binary system to coalesce into one star.
Once they have exhausted their supply of hydrogen through nuclear fusion, medium- to low-mass stars shed their outer layers to form a planetary nebula and evolve into white dwarfs. While most clusters become dispersed before a large proportion of their members have reached the white dwarf stage, the number of white dwarfs in open clusters is still generally much lower than would be expected, given the age of the cluster and the expected initial mass distribution of the stars. One possible explanation for the lack of white dwarfs is that when a red giant expels its outer layers to become a planetary nebula, a slight asymmetry in the loss of material could give the star a ‘kick’ of a few kilometers per second, enough to eject it from the cluster.
Many open clusters are inherently unstable, with a small enough mass that the escape velocity of the system is lower than the average velocity of the constituent stars. These clusters will rapidly disperse within a few million years. In many cases, the stripping away of the gas from which the cluster formed by the radiation pressure of the hot young stars reduces the cluster mass enough to allow rapid dispersal.
Clusters that have enough mass to be gravitationally bound once the surrounding nebula has evaporated can remain distinct for many tens of millions of years, but over time internal and external processes tend also to disperse them. Internally, close encounters between stars can increase the velocity of a member beyond the escape velocity of the cluster. This results in the gradual ‘evaporation’ of cluster members.
Externally, about every half-billion years or so an open cluster tends to be disturbed by external factors such as passing close to or through a molecular cloud. The gravitational tidal forces generated by such an encounter tend to disrupt the cluster. Eventually, the cluster becomes a stream of stars, not close enough to be a cluster but all related and moving in similar directions at similar speeds. The timescale over which a cluster disrupts depends on its initial stellar density, with more tightly packed clusters persisting for longer.
2-MASS SURVEY
The Two Micron All-Sky Survey, or 2MASS, was an astronomical survey of the whole sky in the infrared spectrum and one of the most ambitious projects to do so. It took place between 1997 and 2001, in two different locations, each using a 1.3-meter telescope for the Northern and Southern Hemisphere. It was conducted in the short-wavelength infrared at distinct frequency bands near 2 micrometers.
The immediate scientific benefits from the 2MASS survey include:
1. An unprecedented view of the Milky Way nearly free of the obscuring effects of interstellar dust, which will reveal the true distribution of luminous mass, and thus the largest structures, over the entire length of the Galaxy.
2. The statistical basis to search for rare but astrophysically important objects, which are either cool, and thus extremely red (e.g., extremely low-luminosity stars and brown dwarfs), or heavily obscured at optical wavelengths (e.g., dust-obscured AGNs and globular clusters located in the Galactic plane).
3. To find and catalogue astronomical objects emitting very low levels of light, barely visible with optic telescopes.
2MASS produced an astronomical catalog with over 300 million observed objects, including minor planets of the Solar System, brown dwarfs, low-mass stars, nebulae, star clusters and galaxies. In addition, 1 million objects were cataloged in the 2MASS Extended Source Catalog - including what is believed to be the first directly imaged exo-planet. 2M1207, 2M1207A or 2MASS J12073346-3932539 is a brown dwarf located in the constellation Centaurus; a companion object, 2M1207b, may be the first extrasolar planetary-mass companion to be directly imaged, and is the first discovered orbiting a brown dwarf. Objects cataloged during the 2MASS project are designated with a “2MASS”-prefix.
AETHER OPEN CLUSTER - A GALACTIC ANOMALY
In Parabolus’ Aether Open Cluster, the F-Class stars all contained the 2MASS designation, indicating they were first observed and recorded as part of the 2MASS observation. As such, it is likely that these stars were relatively dim compared to their equal-temperature counterparts. Cmdr Parabolus’ direct observation confirmed this hypothesis, indicating that this Open Cluster is unique in its stellar formation of dim F-Class stars paired with fewer, yet hotter and brighter, B-Class stars. This observation is likely the effect of the Cluster’s location within a galactic void - distant from the denser star forming regions of the galactic spiral arms. As such, the molecular cloud / nebula through which this Parabolus’ cluster was formed was less dense - resulting in dimmer F-Class Stars compared to those found in the arms. The Aether Open Cluster is therefore a galactic anomaly, where Parabolus’ observations confirmed their likely formation - and the rarity of an open cluster located outside of the dense galactic arms.
The Aether Cluster contains the following types of stars:
• F-Class
F5 V [All F-Class stars are F5 V stars created 9.6 billion years ago]
• B-Class
5 Stars Total [B5 III Giant / B6 III Giant / B6 IV SubGiant / B5 V / B2 V]
Y CLASS & T CLASS STAR DISTRIBUTION
The SHEPARD Mission took us through a region of space that contained many non-sequence stars between Waypoints 3 & 5. Sometimes called the Badlands, there is a vast, thin band of L, T, and Y-type Brown Dwarf stars that spans roughly -22LY to -47LY below the Sol Galactic Plane [Sol is used as 0ly reference]. This location is extremely close to the center of the Sag A* Galactic Plane [Sag A* is -21ly below Sol]. The pilots of SHEPARD set off to find out why. What can we observe about star distribution that may shed light on stellar formation and the history of the Milky Way.
Brown dwarfs are star-like objects but are much less massive (with less than 7% of the Sun’s mass), and do not generate internal heat through nuclear fusion like stars. Brown dwarfs simply cool and fade with time and very old brown dwarfs become very cool indeed - the new discoveries have temperatures of 250-600 degrees Celsius, much cooler than stars (in comparison the Sun has a surface temperature of 5600 degrees Celsius).
Stars near to the Sun (in the so-called local volume) are made up of 3 overlapping populations - the thin disk, the thick disk and the halo. The thick disk is much older than the thin disk, and its stars move up and down at a higher velocity. Both these disk components sit within the halo that contains the remnants of the first stars that formed in the Galaxy. There are thought to be as many as 70 billion brown dwarfs in the Galaxy’s thin disk. Moreover, while the thick disk and halo occupy much larger Galactic volumes, only 3 in 100 stars in these regions are brown dwarfs - the most ancient in the Galaxy.
Most stars are formed near or slightly below the galactic plane where the mass of the Milky Way is the highest. As such, it is likely that the star forming attitude of the galaxy, known as the Thin Disk [-50LY to -20LY] would bear most of these Browns Dwarfs, who have hung around near their origin. As stars age, they interact with each other gravitationally and get propelled higher and higher above the central plane, oscillating up and down, like a merry-go-round with ever increasing amplitude.
Most stars that form in our galaxy are now thought to be lower mass brown dwarfs. Whereas Brown Dwarfs are relatively young and contain little mass, larger more massive stars flourished in their early stages of formation and have since traversed their way to the outer regions of the Milky Way. This is why we see a higher percentage population of mature relics of high mass stars in the Thick Disk & Halo [periphery regions of the galaxy], such as Giants & Supergiants, Neutron Stars, Black Holes, & White Dwarfs. These objects have been around since the early stages of the Milky Way’s formation. As such, they have had the requisite time and mass to stretch to these outer regions. The result is that newer, less massive stars, tend to be much more common near the galactic plane. The high density of Brown Dwarfs, in particular L-Class Dwarfs, illustrates this relationship - giving us a temporal understanding of our galaxy - from its inception to present day.
G-CLASS & K-CLASS STELLAR DISTRIBUTION @ NGC 3199 NEBULA
The NGC 3199 Nebula was not an official waypoint of the SHEPARD Mission. Its proximity, however, to the Eta Carina Nebula & GCRV 6807 planetary nebula made it a point of interest that mane SHEPARD cmdrs explored.
NGC 3199 is a large red reflection nebula on the edge of the Orion Shallows - marking the point where the Centaurus Arm makes a dramatic bend to the galactic north. In astronomy, reflection nebulae are clouds of interstellar dust which reflect light of nearby stars. The energy from the nearby stars is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible. Thus, the frequency spectrum shown by reflection nebulae is similar to that of the illuminating stars. Among the microscopic particles responsible for the scattering are carbon compounds and other elements such as iron and nickel. The latter two are often aligned with the galactic magnetic field and cause the scattered light to be slightly polarized.
A large nebula situated approx. 15,000 LYs along the Orion Spur, NGC 3199 was extensively explored and surveyed during a long-range mission along the Orion Spur in March 3301. In the fall of 3301 the nebula was revisited by the Sagittarius-Carina Mission. NGC 3199 looks similar to many nebula closer to Sol, most notably - California, and Heart and Soul. That being said, Cmdr Parabolus of the SHEPARD Mission noticed a very peculiar geometrical star formation around its perimeter - not recorded by either previous expedition.
According to my computer’s galactic map, and Parabolus’ visual observation, the nebula is engrossed in a cluster of K and G type stars in the form of a cube. The perfect cube encloses and is centered around the nebula fully - with roughly equidistant space between the cube edges and the galaxy itself. While this is likely a coincidence, it is possible that something from within the Nebula may be resonating a sub-sonic harmonic vibration, causing the stars to cluster in such a perfect geometric shape. Further observation indicated that there is actually a Wolf-Rayet star within the nebula, HD 89358. [VERIFY IN GAME WOLF-RAYET - near Nebula] Wolf-Rayet stars are very large, massive stars [stars which are about 20 times bigger than the sun] nearly at the end of their stellar lives. As these stars age, material which the stars have cooked up in their central nuclear furnaces (like carbon and oxygen) gradually reach the surface of the star. When enough material reaches the surface, it absorbs so much of the intense light from the star that an enormously strong wind starts to blow from the star’s surface. This wind becomes so thick that it totally obscures the star – so when we look at a Wolf-Rayet star, we’re really just seeing this thick wind. The amount of material which the wind carries away is very large – typically, a mass equivalent to that of the entire earth is lost from the star each year. The mass loss is so large that it significantly shortens the star’s life, and has important effects on the space surrounding the star too.
Could the powerful stellar winds from the Wolf-Rayet actually be causing this cubic morphological composition of these stars?
T TAURI FORMATION @ NGC 3199 NEBULA
Furthermore, my observations of the nebula also indicated a rich star forming just off the far side of the nebula - over a dozen T-Tauri Class stars have recently formed here (what appears to be the dark side). [GET AGE] The oddity is that these star forming sub-clusters only appear on the dark side - as the bright side facing the core only had 3 T-Tauri stars.
T Tauri stars (TTS) are a class of variable stars named after their prototype – T Tauri. They are the youngest visible F, G, K, M spectral type stars. Their surface temperatures are similar to those of main-sequence stars of the same mass, but they are significantly more luminous because their radii are larger. Their central temperatures, however, are too low for hydrogen fusion. Instead, T Tauri stars are powered by gravitational energy released as the stars contract, while moving towards the main sequence, which they reach after about 100 million years. This contraction causes them to rotate typically with a period between one and twelve days, compared to a month for the Sun.
T Tauri stars are found near molecular clouds and identified by their optical variability and strong chromospheric lines. T Tauri stars are pre-main-sequence stars in the process of contracting to the main sequence. The T Tauri stage ends when the protostar develops a radiative zone, or when a larger star commences nuclear fusion on the main sequence. As such, T Tauri protostars are some of the youngest observable objects in our galaxy.
To understand the distribution of T Tauri stars at NGC 3199, we must first understand how stars are typical born.
PROTOSTAR FORMATION
Stars form inside relatively dense concentrations of interstellar gas and dust known as molecular clouds - in many cases these are nebula or regions of nebula. Extremely cold, these dense molecular clouds have a temperature about 10 to 20K - just above absolute zero. At these temperatures have an effect down to the chemical level, where elemental gases form into molecules, meaning that different atoms bind together. CO and H2 are the most common molecules in interstellar gas clouds. As these molecules form, the deep cold also causes the gas to clump into pockets of high densities. As these star farming clouds become more dense, they also become opaque to visible light. As such, there are often referred to as dark nebula.
The NGC 3199 nebula exhibits these same characteristics, insofar as it is composed of a light side and dark side. Furthermore, since star formation begins when the denser parts of the cloud collapse under their own weight/gravity, it seems likely that most protostars would therefore be located in or immediately adjacent to these darker regions - as they tend to be more dense. As such, it is likely that NGC 3199 is symptomatic of the star formation process, where one side is more dense [and subsequently darker]. This disparity between density is likely the cause for the different amounts of T Tauri protostars on either side of the nebula. Cmdr Parabolus’ observations confirmed what we believe we know about the creation of stars and their clustering in certain regions. The result is the non-uniform distribution of star formation around the different sides of the nebula.
NGC 3199, however, is unique insofar as it exhibits the inconsistency of distribution of T-Tauri stars, juxtaposed by the almost uniform distribution of the K & G Cube is perplexing. It is likely that NGC 3199 is a confluence of two unrelated astronomical events:
1. Stellar winds from Wolf-Rayet affecting star clustering of main sequence stars K Class & G Class into an almost perfect cube around the perimeter of the nebula.
2. Non-uniformity of gases into a dense dark region and sparse light region, resulting in a disparity of protostar formation.
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SCIENCE REPORT
REPORT I / LEG 1
4 JANUARY, 3303
PREFACE:
The S.H.E.P.A.R.D Mission of interstellar discovery is named in honor of Alan Shepard, the second human to enter space, and one of only twelve humans to land on the moon during the historic Apollo Missions. Our mission is to obtain scientific data - to observe, document, and collect three primary types of deep space measurements. There are 5 Legs of the SHEPARD Mission. At the completion of each Leg a report will be filed outlining the given scientific findings during each respective Leg. This report, Issue 1, covers Leg-1 of the SHEPARD Mission.
LEG 1 [ORION SPUR & SURROUNDS]:
Leg 1 of the Shepard Mission is a local detailed scan of observable galactic anomalies. It is the aim of Leg 1 of the mission to gather precise data obtainable through detailed surface scans of nearby nebula and star systems. Leg 1 will feature accumulation of data on extremely large red-giant stars, nebulae clusters around Barnard’s Loop, and exhaustive examination of two crucial deep blue planetary nebula. At the end of Leg 1, the crew will perform the first of three Deep-Image-Scans of the galactic core.
GIANTS & STAR CLASSIFICATIONS
Leg-1 of the SHEPARD Mission included detailed scans of many Giant Stars, including the famous Betelgeuse, Rigel, and VY Canis Majoris. This leg, however, also included the discovery of over 20 additional giants hitherto undiscovered. During this process, we learned the basic mechanics of star classification regarding spectra and luminosity - and also discovered two inconsistencies regarding Blue-Supergiants.
STELLAR CLASSIFICATION
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with absorption lines. Each line indicates an ion of a certain chemical element, with the line strength indicating the abundance of that ion. The relative abundance of the different ions varies with the temperature of the photosphere. The spectral class of a star is a short code summarizing the ionization state, giving an objective measure of the photosphere’s temperature and density.
Most stars are currently classified under the Morgan–Keenan (MK) system using the letters O, B, A, F, G, K, and M, a sequence from the hottest (O type) to the coolest (M type). Each letter class is then subdivided using a numeric digit with 0 being hottest and 9 being coolest (e.g. A8, A9, F0, F1 form a sequence from hotter to cooler). The sequence has been expanded with classes for other stars and star-like objects that do not fit in the classical system, such as class D for white dwarfs and class C for carbon stars.
In the MK system, a luminosity class is added to the spectral class using Roman numerals. This is based on the width of certain absorption lines in the star’s spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs. Luminosity class 0 or Ia+ stars for hypergiants, class I stars for supergiants, class II for bright giants, class III for regular giants, class IV for sub-giants, class V for main-sequence stars, class sd for sub-dwarfs, and class D for white dwarfs.
The full spectral class for the Sun is then G2V, indicating a main-sequence star with a temperature around 5,800 K and average luminosity ‘V’.
Following Morgan-Keenan, there are often further sub-classifications regarding luminosity, represented by the letters A&B. A number of different luminosity classes are distinguished for all stellar classes as follows:
0 or Ia+ (hypergiants or extremely luminous supergiants).
Ia (luminous supergiants).
Iab (intermediate luminous supergiants)
Ib (less luminous supergiants)
*While Supergiants are used for example, this division using A&B for luminosity occurs with all luminosity classes from I-VII.
The pilots of SHEPARD have encountered two anomalies with the galactic naming of supergiants on board ships’ computer galactic maps.
1. A giant star is a star with substantially larger radius and luminosity than a main-sequence (or dwarf) star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsprung–Russell diagram and correspond to luminosity classes II and III. The terms giant and dwarf were coined for stars of quite different luminosity despite similar temperature or spectral type by Ejnar Hertzsprung about 1905. Giant stars have radii up to a few hundred times the Sun and luminosities between 10 and a few thousand times that of the Sun. Stars still more luminous than giants are referred to as supergiants and hypergiants.
Stars designated as Blue-White [A / B / O] do not follow the same naming standard in the ship’s computer galmap, insofar as class III Giants are not listed as ‘Giants’. While White & Blue class III giants are rare [often not depicted on many Hertzsprung–Russell diagrams], they still satisfy the criteria of a Giant Star. The galmap correctly identifies K & M class III as giants [orange and red respectively], however counts A, B, & O III giants and IV subgaints as normal stars.
2. B-Class Supergiants [Class I & II] are mislabeled as A-Class Supergiants. This error occurs both in the galactic map screen as well as during FSD initiation when the nav-com reports the destination system. Looking at the detailed information about the given star, however, will indicate that the star is actually a B-Class. Cmdrs are encouraged to inspect both systems to ensure star-classification is correct.
OPEN CLUSTERS & 2MASS STARS
Perhaps the most prominent Open Cluster of stars in the galaxy was the first waypoint of SHEPARD - The Orion Nebula [others include NGC 7822]. Because the Orion Nebula is adjacent to the inhabited bubble, the pilots of SHEPARD have set out to discover new stellar clusters in an attempt to understand more about how they are formed, what ties them together, and what type of stars are most commonly distributed. Finding other open clusters may help us know more about our neighbor the Orion Nebula cluster.
OPEN CLUSTERS
During Leg-1 Cmdr Parabolus located an relatively unexplored open stellar cluster of F-Class stars well below the galactic plane. The cluster was made of roughly 70% F-Class stars and 30% B-Class. The F-Class stars were all designated with the prefix 2MASS, indicating that they were first discovered during the 2MASS observation of the late 20th century [see page 11]. This strange ‘stellar pillar,’ as Parabolus described it, was located in the Sagittarius Gap. Parabolus has since named it the Aether Cluster, after the Greek God Aether. Aether in ancient Greece was one of the primordial deities. Aether is the personification of the upper air. He embodies the pure upper air that the gods breathe, as opposed to the normal air breathed by mortals.
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist. They are loosely bound by mutual gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the galactic center. This can result in a migration to the main body of the galaxy and a loss of cluster members through internal close encounters. Open clusters generally survive for a few hundred million years, with the most massive ones surviving for a few billion years. In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, and can survive for longer. Open clusters have been found only in spiral and irregular galaxies, in which active star formation is occurring.
Young open clusters may not be contained within the molecular cloud from which they formed. Over time, radiation pressure from the cluster will disperse the molecular cloud. Typically, about 10% of the mass of a gas cloud will coalesce into stars before radiation pressure drives the rest of the gas away.
Open clusters are key objects in the study of stellar evolution. Because the cluster members are of similar age and chemical composition, their properties [such as distance, age, metallicity and extinction] are more easily determined than they are for isolated stars. A number of open clusters, such as the Pleiades, Hyades or the Alpha Persei Cluster are visible with the naked eye. Some others, such as the Double Cluster, are barely perceptible without instruments.
The formation of an open cluster begins with the collapse of part of a giant molecular cloud, a cold dense cloud of gas and dust containing up to many thousands of times the mass of the Sun. These clouds have densities that vary from 102 to 106 molecules of neutral hydrogen per cm3, with star formation occurring in regions with densities above 104 molecules per cm3. Typically, only 1–10% of the cloud by volume is above the latter density. Prior to collapse, these clouds maintain their mechanical equilibrium through magnetic fields, turbulence, and rotation.
Many factors may disrupt the equilibrium of a giant molecular cloud, triggering a collapse and initiating the burst of star formation that can result in an open cluster. These include shock waves from a nearby supernova, collisions with other clouds, or gravitational interactions. Even without external triggers, regions of the cloud can reach conditions where they become unstable against collapse. The collapsing cloud region will undergo hierarchical fragmentation into ever smaller clumps, including a particularly dense form known as infrared dark clouds, eventually leading to the formation of up to several thousand stars. This star formation begins enshrouded in the collapsing cloud, blocking the protostars from sight but allowing infrared observation. In the Milky Way galaxy, the formation rate of open clusters is estimated to be one every few thousand years.
It is common for two or more separate open clusters to form out of the same molecular cloud. In the Large Magellanic Cloud, both Hodge 301 and R136 are forming from the gases of the Tarantula Nebula, while in our own galaxy, tracing back the motion through space of the Hyades and Praesepe, two prominent nearby open clusters, suggests that they formed in the same cloud about 600 million years ago. Sometimes, two clusters born at the same time will form a binary cluster. The best known example in the Milky Way is the Double Cluster of NGC 869 and NGC 884 but at least 10 more double clusters are known to exist. Many more are known in the Small and Large Magellanic Clouds—they are easier to detect in external systems than in our own galaxy because projection effects can cause unrelated clusters within the Milky Way to appear close to each other.
There are over 1,000 known open clusters in our galaxy, but the true total may be up to ten times higher than that. In spiral galaxies, open clusters are largely found in the spiral arms where gas densities are highest and so most star formation occurs, and clusters usually disperse before they have had time to travel beyond their spiral arm. Open clusters are strongly concentrated close to the galactic plane. The Aether Open Cluster that Parabolus located is an anomaly - insofar as it was well below the galactic plane and not located within a spiral arm, but rather in the less dense void between them.
The center of the Aether Cluster featured a large class B Star - with an M-Class star orbiting it. What is curious about this stellar pillar is that it is location in Sagittarius Gap - a void between arms. While at first thought one might assume that there might be some sort of invisible gravitational anomaly present in the region - causing these stars to cluster up together, we believe they were actually created in this formation - an echo of a former pulsar nebula whose glowing gases have since blown away - leaving only these relatively dim F class stars amidst five large B-Class brethren. At some point there may have been a super-massive stellar explosion at this location in the very distant past.
Parabolus’ discovery got the pilots of SHEPARD interested in the clustering phenomenon, in the hope that we may understand more about their formation in relation to nebulae. We hope to locate more undiscovered clusters further along in our journey.
STELLAR COMPOSITION AND FATE OF OPEN CLUSTERS
Because open clusters tend to be dispersed before most of their stars reach the end of their lives, the light from them tends to be dominated by the young, hot blue stars. These stars are the most massive, and have the shortest lives of a few tens of millions of years. The older open clusters tend to contain more yellow stars. When a Hertzsprung-Russell diagram is plotted for an open cluster, most stars lie on the main sequence. The most massive stars have begun to evolve away from the main sequence and are becoming red giants; the position of the turn-off from the main sequence can be used to estimate the age of the cluster.
Because the stars in an open cluster are all at roughly the same distance from Earth, and were born at roughly the same time from the same raw material, the differences in apparent brightness among cluster members is due only to their mass. This makes open clusters very useful in the study of stellar evolution, because when comparing one star to another, many of the variable parameters are fixed.
Some open clusters contain hot blue stars which seem to be much younger than the rest of the cluster. These blue stragglers are also observed in globular clusters, and in the very dense cores of globulars they are believed to arise when stars collide, forming a much hotter, more massive star. However, the stellar density in open clusters is much lower than that in globular clusters, and stellar collisions cannot explain the numbers of blue stragglers observed. Instead, it is thought that most of them probably originate when dynamical interactions with other stars cause a binary system to coalesce into one star.
Once they have exhausted their supply of hydrogen through nuclear fusion, medium- to low-mass stars shed their outer layers to form a planetary nebula and evolve into white dwarfs. While most clusters become dispersed before a large proportion of their members have reached the white dwarf stage, the number of white dwarfs in open clusters is still generally much lower than would be expected, given the age of the cluster and the expected initial mass distribution of the stars. One possible explanation for the lack of white dwarfs is that when a red giant expels its outer layers to become a planetary nebula, a slight asymmetry in the loss of material could give the star a ‘kick’ of a few kilometers per second, enough to eject it from the cluster.
Many open clusters are inherently unstable, with a small enough mass that the escape velocity of the system is lower than the average velocity of the constituent stars. These clusters will rapidly disperse within a few million years. In many cases, the stripping away of the gas from which the cluster formed by the radiation pressure of the hot young stars reduces the cluster mass enough to allow rapid dispersal.
Clusters that have enough mass to be gravitationally bound once the surrounding nebula has evaporated can remain distinct for many tens of millions of years, but over time internal and external processes tend also to disperse them. Internally, close encounters between stars can increase the velocity of a member beyond the escape velocity of the cluster. This results in the gradual ‘evaporation’ of cluster members.
Externally, about every half-billion years or so an open cluster tends to be disturbed by external factors such as passing close to or through a molecular cloud. The gravitational tidal forces generated by such an encounter tend to disrupt the cluster. Eventually, the cluster becomes a stream of stars, not close enough to be a cluster but all related and moving in similar directions at similar speeds. The timescale over which a cluster disrupts depends on its initial stellar density, with more tightly packed clusters persisting for longer.
2-MASS SURVEY
The Two Micron All-Sky Survey, or 2MASS, was an astronomical survey of the whole sky in the infrared spectrum and one of the most ambitious projects to do so. It took place between 1997 and 2001, in two different locations, each using a 1.3-meter telescope for the Northern and Southern Hemisphere. It was conducted in the short-wavelength infrared at distinct frequency bands near 2 micrometers.
The immediate scientific benefits from the 2MASS survey include:
1. An unprecedented view of the Milky Way nearly free of the obscuring effects of interstellar dust, which will reveal the true distribution of luminous mass, and thus the largest structures, over the entire length of the Galaxy.
2. The statistical basis to search for rare but astrophysically important objects, which are either cool, and thus extremely red (e.g., extremely low-luminosity stars and brown dwarfs), or heavily obscured at optical wavelengths (e.g., dust-obscured AGNs and globular clusters located in the Galactic plane).
3. To find and catalogue astronomical objects emitting very low levels of light, barely visible with optic telescopes.
2MASS produced an astronomical catalog with over 300 million observed objects, including minor planets of the Solar System, brown dwarfs, low-mass stars, nebulae, star clusters and galaxies. In addition, 1 million objects were cataloged in the 2MASS Extended Source Catalog - including what is believed to be the first directly imaged exo-planet. 2M1207, 2M1207A or 2MASS J12073346-3932539 is a brown dwarf located in the constellation Centaurus; a companion object, 2M1207b, may be the first extrasolar planetary-mass companion to be directly imaged, and is the first discovered orbiting a brown dwarf. Objects cataloged during the 2MASS project are designated with a “2MASS”-prefix.
AETHER OPEN CLUSTER - A GALACTIC ANOMALY
In Parabolus’ Aether Open Cluster, the F-Class stars all contained the 2MASS designation, indicating they were first observed and recorded as part of the 2MASS observation. As such, it is likely that these stars were relatively dim compared to their equal-temperature counterparts. Cmdr Parabolus’ direct observation confirmed this hypothesis, indicating that this Open Cluster is unique in its stellar formation of dim F-Class stars paired with fewer, yet hotter and brighter, B-Class stars. This observation is likely the effect of the Cluster’s location within a galactic void - distant from the denser star forming regions of the galactic spiral arms. As such, the molecular cloud / nebula through which this Parabolus’ cluster was formed was less dense - resulting in dimmer F-Class Stars compared to those found in the arms. The Aether Open Cluster is therefore a galactic anomaly, where Parabolus’ observations confirmed their likely formation - and the rarity of an open cluster located outside of the dense galactic arms.
The Aether Cluster contains the following types of stars:
• F-Class
F5 V [All F-Class stars are F5 V stars created 9.6 billion years ago]
• B-Class
5 Stars Total [B5 III Giant / B6 III Giant / B6 IV SubGiant / B5 V / B2 V]
Y CLASS & T CLASS STAR DISTRIBUTION
The SHEPARD Mission took us through a region of space that contained many non-sequence stars between Waypoints 3 & 5. Sometimes called the Badlands, there is a vast, thin band of L, T, and Y-type Brown Dwarf stars that spans roughly -22LY to -47LY below the Sol Galactic Plane [Sol is used as 0ly reference]. This location is extremely close to the center of the Sag A* Galactic Plane [Sag A* is -21ly below Sol]. The pilots of SHEPARD set off to find out why. What can we observe about star distribution that may shed light on stellar formation and the history of the Milky Way.
Brown dwarfs are star-like objects but are much less massive (with less than 7% of the Sun’s mass), and do not generate internal heat through nuclear fusion like stars. Brown dwarfs simply cool and fade with time and very old brown dwarfs become very cool indeed - the new discoveries have temperatures of 250-600 degrees Celsius, much cooler than stars (in comparison the Sun has a surface temperature of 5600 degrees Celsius).
Stars near to the Sun (in the so-called local volume) are made up of 3 overlapping populations - the thin disk, the thick disk and the halo. The thick disk is much older than the thin disk, and its stars move up and down at a higher velocity. Both these disk components sit within the halo that contains the remnants of the first stars that formed in the Galaxy. There are thought to be as many as 70 billion brown dwarfs in the Galaxy’s thin disk. Moreover, while the thick disk and halo occupy much larger Galactic volumes, only 3 in 100 stars in these regions are brown dwarfs - the most ancient in the Galaxy.
Most stars are formed near or slightly below the galactic plane where the mass of the Milky Way is the highest. As such, it is likely that the star forming attitude of the galaxy, known as the Thin Disk [-50LY to -20LY] would bear most of these Browns Dwarfs, who have hung around near their origin. As stars age, they interact with each other gravitationally and get propelled higher and higher above the central plane, oscillating up and down, like a merry-go-round with ever increasing amplitude.
Most stars that form in our galaxy are now thought to be lower mass brown dwarfs. Whereas Brown Dwarfs are relatively young and contain little mass, larger more massive stars flourished in their early stages of formation and have since traversed their way to the outer regions of the Milky Way. This is why we see a higher percentage population of mature relics of high mass stars in the Thick Disk & Halo [periphery regions of the galaxy], such as Giants & Supergiants, Neutron Stars, Black Holes, & White Dwarfs. These objects have been around since the early stages of the Milky Way’s formation. As such, they have had the requisite time and mass to stretch to these outer regions. The result is that newer, less massive stars, tend to be much more common near the galactic plane. The high density of Brown Dwarfs, in particular L-Class Dwarfs, illustrates this relationship - giving us a temporal understanding of our galaxy - from its inception to present day.
G-CLASS & K-CLASS STELLAR DISTRIBUTION @ NGC 3199 NEBULA
The NGC 3199 Nebula was not an official waypoint of the SHEPARD Mission. Its proximity, however, to the Eta Carina Nebula & GCRV 6807 planetary nebula made it a point of interest that mane SHEPARD cmdrs explored.
NGC 3199 is a large red reflection nebula on the edge of the Orion Shallows - marking the point where the Centaurus Arm makes a dramatic bend to the galactic north. In astronomy, reflection nebulae are clouds of interstellar dust which reflect light of nearby stars. The energy from the nearby stars is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible. Thus, the frequency spectrum shown by reflection nebulae is similar to that of the illuminating stars. Among the microscopic particles responsible for the scattering are carbon compounds and other elements such as iron and nickel. The latter two are often aligned with the galactic magnetic field and cause the scattered light to be slightly polarized.
A large nebula situated approx. 15,000 LYs along the Orion Spur, NGC 3199 was extensively explored and surveyed during a long-range mission along the Orion Spur in March 3301. In the fall of 3301 the nebula was revisited by the Sagittarius-Carina Mission. NGC 3199 looks similar to many nebula closer to Sol, most notably - California, and Heart and Soul. That being said, Cmdr Parabolus of the SHEPARD Mission noticed a very peculiar geometrical star formation around its perimeter - not recorded by either previous expedition.
According to my computer’s galactic map, and Parabolus’ visual observation, the nebula is engrossed in a cluster of K and G type stars in the form of a cube. The perfect cube encloses and is centered around the nebula fully - with roughly equidistant space between the cube edges and the galaxy itself. While this is likely a coincidence, it is possible that something from within the Nebula may be resonating a sub-sonic harmonic vibration, causing the stars to cluster in such a perfect geometric shape. Further observation indicated that there is actually a Wolf-Rayet star within the nebula, HD 89358. [VERIFY IN GAME WOLF-RAYET - near Nebula] Wolf-Rayet stars are very large, massive stars [stars which are about 20 times bigger than the sun] nearly at the end of their stellar lives. As these stars age, material which the stars have cooked up in their central nuclear furnaces (like carbon and oxygen) gradually reach the surface of the star. When enough material reaches the surface, it absorbs so much of the intense light from the star that an enormously strong wind starts to blow from the star’s surface. This wind becomes so thick that it totally obscures the star – so when we look at a Wolf-Rayet star, we’re really just seeing this thick wind. The amount of material which the wind carries away is very large – typically, a mass equivalent to that of the entire earth is lost from the star each year. The mass loss is so large that it significantly shortens the star’s life, and has important effects on the space surrounding the star too.
Could the powerful stellar winds from the Wolf-Rayet actually be causing this cubic morphological composition of these stars?
T TAURI FORMATION @ NGC 3199 NEBULA
Furthermore, my observations of the nebula also indicated a rich star forming just off the far side of the nebula - over a dozen T-Tauri Class stars have recently formed here (what appears to be the dark side). [GET AGE] The oddity is that these star forming sub-clusters only appear on the dark side - as the bright side facing the core only had 3 T-Tauri stars.
T Tauri stars (TTS) are a class of variable stars named after their prototype – T Tauri. They are the youngest visible F, G, K, M spectral type stars. Their surface temperatures are similar to those of main-sequence stars of the same mass, but they are significantly more luminous because their radii are larger. Their central temperatures, however, are too low for hydrogen fusion. Instead, T Tauri stars are powered by gravitational energy released as the stars contract, while moving towards the main sequence, which they reach after about 100 million years. This contraction causes them to rotate typically with a period between one and twelve days, compared to a month for the Sun.
T Tauri stars are found near molecular clouds and identified by their optical variability and strong chromospheric lines. T Tauri stars are pre-main-sequence stars in the process of contracting to the main sequence. The T Tauri stage ends when the protostar develops a radiative zone, or when a larger star commences nuclear fusion on the main sequence. As such, T Tauri protostars are some of the youngest observable objects in our galaxy.
To understand the distribution of T Tauri stars at NGC 3199, we must first understand how stars are typical born.
PROTOSTAR FORMATION
Stars form inside relatively dense concentrations of interstellar gas and dust known as molecular clouds - in many cases these are nebula or regions of nebula. Extremely cold, these dense molecular clouds have a temperature about 10 to 20K - just above absolute zero. At these temperatures have an effect down to the chemical level, where elemental gases form into molecules, meaning that different atoms bind together. CO and H2 are the most common molecules in interstellar gas clouds. As these molecules form, the deep cold also causes the gas to clump into pockets of high densities. As these star farming clouds become more dense, they also become opaque to visible light. As such, there are often referred to as dark nebula.
The NGC 3199 nebula exhibits these same characteristics, insofar as it is composed of a light side and dark side. Furthermore, since star formation begins when the denser parts of the cloud collapse under their own weight/gravity, it seems likely that most protostars would therefore be located in or immediately adjacent to these darker regions - as they tend to be more dense. As such, it is likely that NGC 3199 is symptomatic of the star formation process, where one side is more dense [and subsequently darker]. This disparity between density is likely the cause for the different amounts of T Tauri protostars on either side of the nebula. Cmdr Parabolus’ observations confirmed what we believe we know about the creation of stars and their clustering in certain regions. The result is the non-uniform distribution of star formation around the different sides of the nebula.
NGC 3199, however, is unique insofar as it exhibits the inconsistency of distribution of T-Tauri stars, juxtaposed by the almost uniform distribution of the K & G Cube is perplexing. It is likely that NGC 3199 is a confluence of two unrelated astronomical events:
1. Stellar winds from Wolf-Rayet affecting star clustering of main sequence stars K Class & G Class into an almost perfect cube around the perimeter of the nebula.
2. Non-uniformity of gases into a dense dark region and sparse light region, resulting in a disparity of protostar formation.
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