Local Star Formation Studies from SPYGLASS
Local star formation studies select an individual population or set of populations and searches for star formation patterns at the population scale, providing insight into the processes that guide the progression of star formation. These studies rely on dynamical traceback, where we use high-quality position and velocity measurements from both the Gaia spacecraft and independent spectroscopic measurements to compute past stellar positions. The results show not just the positions of subgroups relative to each other, but also the dispersal of stars after formation, with the moment of closest configuration indicating subgroup age. We refine these ages using other methods, providing a comprehensive view of the locations of stars at the times of formation, and how the populations relate to each other. Several patterns have emerged through this work:
-
Stellar associations that are widely distributed in the present-day often trace back to compact star-forming sites consistent with a single cloud, which we refer to as star formation "nodes".
-
Star-forming regions often contain more than one node.
-
Star formation often lasts upwards of 10 Myr, even within individual nodes in relatively low-mass young associations.
-
Age and velocity gradients are incredibly common. Decreasing ages are usually found further from the center of an association in the direction of increasing velocity relative to the population average, consistent with sequences where multiple stellar generations emerge from an accelerating gas cloud
-
Populations with overlapping transverse velocities can have very different radial velocities, so full 6D space-velocity surveys may be necessary to confirm the coherence of an association.
​​​​
I have already published five papers in this category, which you can explore in the links to the right, or in the summaries below. Expect more to come soon, both from me and from undergraduate students I am supervising that are completing related projects.
SPYGLASS Studies of Local Star Formation
SPYGLASS. II. The Multigenerational and Multiorigin Star Formation History of Cepheus Far North
SPYGLASS. III. The Fornax-Horologium Association and Its Traceback History within the Austral Complex
SPYGLASS. V. Spatially and Temporally Structured Star-forming Environments in the Cepheus-Hercules Complex
SPYGLASS. VI. Feedback-driven Star Formation in the Circinus Complex
SPYGLASS. VII-A. The Demographics and Ages of Small Nearby Young Associations
Large Populations within 200 pc
Within 200 pc of the sun, the SPYGLASS-I survey work revealed several relatively large stellar populations with little to no previous literature coverage. To learn about the star formation histories of these little-known by highly accessible populations, I published papers detailing dynamical analyses for the Cepheus Far North (CFN) Association, as well as Fornax-Horologium and the remainder of the Austral Complex, which includes the better-known populations of Tuc-Hor, Carina, and Columba.
Cepheus Far North is one of the largest associations from SPYGLASS-I without widespread previous coverage. To deepen our understanding of this population, we used the 2.7m Harlan J. Smith Telescope at the McDonald Observatory in West Texas to make extensive new radial velocity measurements. Our traceback of members reveals:​​
-
Subgroups form in two distinct nodes – maybe from a fragmenting filament?
-
Star formation across both nodes takes place over a 10 Myr time period, or ~8 Myr in each node.
-
Distribution of ages is consistent with continuous formation
-
EE Dra is a new gravitationally bound open cluster, containing ~10 solar masses within an age of ~27 Myr old.
See the figure below for the complete history of CFN's formation. Stars appear at their moment of formation, and their evolution is shown from 32 Myr ago to the present day. ​
Fornax-Horologium (FH) is centered on the χ1 Fornacis Cluster, and is the nearest SPYGLASS-I association to the Sun. Our study includes Tuc-Hor, Carina, and Columba, which form an extensive and interconnected "Austral Complex". We find:
-
Co-spatial formation for Carina, Columba, and FH, while Tuc-Hor forms in a distinct note, similar to the formation nodes in CFN.
-
Platais 8, a Sco-Cen subgroup in SPYGLASS-I, stays nearby throughout the complex's formation, suggesting that viewing the complex in isolation may miss large-scale patterns and connections.
These studies have revealed a pattern in which associations are composed of multiple discrete star formation nodes that are not obvious in dynamical or spatial coordinates. These nodes of common formation may represent the clearest discrete unit of star formation, and resolving more of them as well as calculating their positions during formation may be critical to the demystification of large-scale star formation patterns
Studies of Larger, Multi-Component Complexes
Several stellar populations identified in SPYGLASS-IV are notably inhomogeneous, with regional disparities in age and in radial velocity. To establish whether these populations have a common origin or whether they formed in entirely distinct star-forming events, I am therefore performing dedicated studies covering locations where my survey work has grouped many known populations into a single complex. I have already published a paper on Cep-Her, shown below, but student projects are underway looking at other regions, including Orion and Vela.
The Cep-Her Complex is the largest stellar population within 500 pc that lacked substantial follow-up when SPYGLASS-IV was published. I therefore conducted a comprehensive survey of the region, revealing that Cep-Her is not just a single association, but rather an amalgam of four. The component associations include the (τ > 100 Myr) open cluster Roslund 6, in addition to three dynamically coherent and highly substructured young associations: Orpheus (25–40 Myr), Cinyras (28–43 Myr), and Cupavo (54–80 Myr). All three newly described associations are among the largest young associations within 500 pc, rivalling major associations like Sco-Cen. Our novel view of the ages and dynamics of these associations reveals evidence for sequential star formation in Cinyras, in addition to a multiorigin pattern of stellar dispersal in Orpheus that may hint to the presence of multiple clouds at formation. The interactive figure below shows the 3D structure of the complex, with the ability to toggle the visibility of the four component associations
My work in Circinus reveals a star formation gradient, with older stellar populations in the centre, and younger populations in the outskirts. This is similar to patterns seen in other populations, including the work on Cep-Her above, where a similar gradient is visible in Cinyras, and the well-studied populations of Sco-Cen and Vela OB2. To better understand how these patterns emerged, I compared the distribution of stars and ages in Circinus to simulations from the STARFORGE suite. The two figures below show the distribution of stellar populations in Circinus (top), and the fiducial 1 simulation from STARFORGE. Both show a clear inside-out star formation pattern, with older stars in the centre and younger stars in the outskirts. Both also show a gradient in velocity, with faster-moving stars further from the centre of the population.
The figures above show a close correspondence between Circinus and the STARFORGE simulations in terms of the total size of the population, presence of a large cluster in the centre, velocity spread relative to the average (~4 km/s for both), age spread, and overall morphology. To investigate how Circinus may have formed, we looked at the progression of star formation in the simulation, which is shown in the video below. This revealed a pattern of core-driven sequential star formation, a new mechanism for sequential star formation where later generations form in a shell driven by feedback from the central cluster, starting with parts of residual filaments most exposed to the central cluster, and propagating outward. This produces a gradient in both space and velocity, since the first generations form so quickly that they reach high enough densities to form stars before they substantially accelerate.
Low-Mass Young Associations
Many young stellar associations in my survey work are very small structures that have seen next to no dedicated research to date. These star-forming regions are therefore almost entirely unstudied, so we know little about what conditions lead to their formation, or whether substructure exists. SPYGLASS-VII studies 15 young associations in this low-mass category, measuring their demographics and ages, and placing these populations within the larger galactic context. There are currently two papers in this mini-series, with the first one published, and the second submitted.
​
In SPYGLASS-VII-A, I combined isochronal, dynamical, and lithium depletion methods to produce robust ages for these associations, and compute their total masses and populations. I also identified substructure, revealing that one association, Taurus-Orion 1, contains two sub-components that formed in entirely distinct locations, which I refer to as TOR1A and B. Low-mass associations are particularly well-suited for dynamical ages, as their apparent isolation limits the risk of nearby gas structures delaying dispersal and biasing those ages, and the small sizes minimize the potential for complicating substructure. The ages of these populations spanned from 7 to 43 Myr, with stellar populations ranging from 34 stars and 16 solar masses in TOR1B to 306 stars in 119 solar masses in SCYA-54. The PARSEC isochrones consistently agreed with other methods, supporting their use in most cases. I also found that including a debias method used in Couture et al. 2023, dynamical ages were consistently within uncertainties of the isochronal ages, opposing the findings of Miret-Roig et al. 2024, which found a ~5 Myr offset.
​​
SPYGLASS-VII-B: the Broader Context
This paper is currently under review, but current results indicate that these low-mass populations often form out of the edges of large, expanding bubbles. We also identify one association that appears to have formed through the collision between a high-velocity cloud and the galactic mid-plane, providing the first evidence that this type of cloud can be star-forming. There are many more exciting findings that will be released with the paper, check back later to learn more!
​​​