arXiv subjects

Debby Tran

Publications and source records attributed to Debby Tran.

6 recordsLinked to original sources

arXiv2026

Automated Computer Vision Cluster Identification in the Fireworks Galaxy

We present the integrated photometry, radii, and spatial distribution of young ($\leq$ 25 Myr) star cluster candidates in NGC 6946. NGC 6946, also known as the Fireworks Galaxy, is a highly star-forming galaxy with numerous young massive clusters. We have developed a modified computer vision algorithm using photometry from images taken with Hubble Space Telescope (HST) Wide Field Camera 3 Ultraviolet channel (WFC3/UVIS) F275W and F336W filters to identify and outline candidate clusters. We describe our technique in detail, including extensive testing with artificial clusters, where the algorithm recovers 60.7% of synthetic clusters and has a conservative false positive rate of 27.3% down to luminosities of M$_{F336W} \sim -6$. We identify 6410 cluster candidates down to much fainter magnitudes (M$_{F336W} \sim -4$) via the aforementioned algorithm which are more difficult to verify, but are still of interest as the luminosity function of these candidates is consistent with a standard power law with a slope of $\sim$2.

astro-ph.GA↗

arXiv2026

The Panchromatic Hubble Andromeda Southern Treasury (PHAST). II. The Spatially Resolved Recent Star Formation History in M31

We use Hubble Space Telescope optical imaging from the Panchromatic Hubble Andromeda Southern Treasury (PHAST) to measure the spatially resolved recent star formation history (SFH) across the southern disk of M31. We fit color-magnitude diagrams (CMDs) of over 6500 individual 0.01 kpc$^2$ regions to measure SFHs over the last $\sim$500 Myr. The resulting maps show coherent structure that traces the ringed morphology of the disk. We find a clear global decline in the recent SFR, with a pronounced drop in the last $\sim$40 Myr that is most evident in the region closest to M32. Combining PHAST and PHAT measurements, we now cover two thirds of M31's star-forming disk with homogeneous SFHs, yielding the highest-resolution spatially resolved SFHs of M31. Inside the joint footprint, we measure mean SFRs of $0.445 \pm0.006$ M$_\odot$ yr$^{-1}$ over the last 100 Myr and $0.285 \pm 0.014$ M$_\odot$ yr$^{-1}$ over the last 20 Myr, implying total disk SFRs of $\sim$0.67 and $\sim$0.43 M$_\odot$ yr$^{-1}$, respectively. The observed decline is interpreted as the late stage of a multi-Gyr wind-down from a previously more active state. Because recent star formation in M31 is concentrated primarily in the rings, the global decline is driven mainly by decreasing activity within those features. We also compare the CMD-based SFR surface densities to those inferred from FUV+24 $\mu$m prescriptions and find that the FUV-based calibration underestimates the CMD-based 100 Myr average by a factor of $\sim$2.1. However, the PHAST SFHs produce a synthetic GALEX FUV image that agrees well with observations, indicating that the CMD-derived SFHs provide an accurate description of recent star formation. The mismatch with the FUV+24 $\mu$m estimates underscores that tracers implicitly averaged over $\sim$100 Myr are not reliable when the recent SFR is evolving.

astro-ph.GA↗

arXiv2023

Considering the Single and Binary Origins of the Type IIP SN 2017eaw

Current population synthesis modeling suggests that 30-50% of Type II supernovae originate from binary progenitors, however, the identification of a binary progenitor is challenging. One indicator of a binary progenitor is that the surrounding stellar population is too old to contain a massive single star.Measurements of the progenitor mass of SN 2017eaw are starkly divided between observations made temporally close to core-collapse which show a progenitor mass of 13-15 solar masses (final helium core mass of 4.4 to 6.0 solar masses - which is a more informative property than initial mass) and those from the stellar population surrounding the SN which find M<10.8 solar masses (helium core mass <3.4 solar masses). In this paper, we reanalyze the surrounding stellar population with improved astrometry and photometry, finding a median age of 16.8 (+3.2, -1.0) Myr for all stars younger than 50 Myr (helium core mass of 4.7 solar masses) and 85.9 (+3.2, -6.5) Myr for stars younger than 150 Myr. 16.8 Myr is now consistent with the helium core mass range derived from the temporally near explosion observations for single stars. Applying the combined constraints to population synthesis models, we determine that the probability of the progenitor of SN 2017eaw being an initially single-star is 65% compared to 35% for prior binary interaction. 85.9 Myr is inconsistent with any formation scenarios. We demonstrate that combining progenitor age constraints with helium core mass estimates from red supergiant SED modeling, late-time spectra, and indirectly from light curve modeling can help to differentiate single and binary progenitor scenarios and provide a framework for the application of this technique to future observations.

astro-ph.HE↗

arXiv2023

Spatially-Resolved Recent Star Formation History in NGC 6946

The nearby face-on star forming spiral galaxy NGC 6946 is known as the Fireworks Galaxy due to its hosting an unusually large number of supernova. We analyze its resolved near-ultraviolet (NUV) stellar photometry measured from images taken with the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) with F275W and F336W filters. We model the color-magnitude diagrams (CMD) of the UV photometry to derive the spatially-resolved star formation history (SFH) of NGC 6946 over the last 25 Myr. From this analysis, we produce maps of the spatial distribution of young stellar populations and measure the total recent star formation rate (SFR) of nearly the entire young stellar disk. We find the global SFR(age$\leq$25 Myr)=$13.17 \substack{+0.91 \\-0.79} M_\odot/\rm yr$. Over this period, the SFR is initially very high ($23.39\substack{+2.43\\-2.11} M_\odot/\rm yr$ between 16-25 Myr ago), then monotonically decreases to a recent SFR of $5.31\substack{+0.19\\-0.17} M_\odot/\rm yr$ in the last 10 Myr. This decrease in global star formation rate over the last 25 Myr is consistent with measurements made with other SFR indicators. We discuss in detail two of the most active regions of the galaxy, which we find are responsible for 3% and 5% of the total star formation over the past 6.3 Myr.

astro-ph.GA↗

arXiv2023

Initial Fabrication and Characterization of Chemically-Etched Silicon Slits for KOSMOS

KOSMOS is a low-resolution, long-slit, optical spectrograph that has been upgraded at the University of Washington for its move from Kitt Peak National Observatory's Mayall 4m telescope to the Apache Point Observatory's ARC 3.5m telescope. One of the additions to KOSMOS is a slitviewer, which requires the fabrication of reflective slits, as KOSMOS previously used matte slits machined via wire EDM. We explore a novel method of slit fabrication using nanofabrication methods and compare the slit edge roughness, width uniformity, and the resulting scattering of the new fabricated slits to the original slits. We find the kerf surface of the chemically-etched reflective silicon slits are generally smoother than the machined matte slits, with an upper limit average roughness of 0.42 $\pm$ 0.03 $μ$m versus 1.06 $\pm$ 0.04 $μ$m respectively. The etched slits have width standard deviations of 6 $\pm$ 3 $μ$m versus 10 $\pm$ 6 $μ$m, respectively. The scattering for the chemically-etched slits is higher than that of the machined slits, showing that the reflectivity is the major contributor to scattering, not the roughness. This scattering, however, can be effectively reduced to zero with proper background subtraction. As slit widths increase, scattering increases for both types of slits, as expected. Future work will consist of testing and comparing the throughput and spectrophotometric data quality of these nanofabricated slits to the machined slits with on-sky data, in addition to making the etched slits more robust against breakage and finalizing the slit manufacturing process.

astro-ph.IM↗

arXiv2015

Astrometric Confirmation and Preliminary Orbital Parameters of the Young Exoplanet 51 Eridani b with the Gemini Planet Imager

We present new Gemini Planet Imager observations of the young exoplanet 51 Eridani b which provide further evidence that the companion is physically associated with 51 Eridani. Combining this new astrometric measurement with those reported in the literature, we significantly reduce the posterior probability that 51 Eridani b is an unbound foreground or background T-dwarf in a chance alignment with 51 Eridani to $2\times10^{-7}$, an order of magnitude lower than previously reported. If 51 Eridani b is indeed a bound object, then we have detected orbital motion of the planet between the discovery epoch and the latest epoch. By implementing a computationally efficient Monte Carlo technique, preliminary constraints are placed on the orbital parameters of the system. The current set of astrometric measurements suggest an orbital semimajor axis of $14^{+7}_{-3}$ AU, corresponding to a period of $41^{+35}_{-12}$ years (assuming a mass of $1.75$ $M_{\odot}$ for the central star), and an inclination of $138^{+15}_{-13}$ deg. The remaining orbital elements are only marginally constrained by the current measurements. These preliminary values suggest an orbit which does not share the same inclination as the orbit of the distant M-dwarf binary, GJ 3305, which is a wide physically bound companion to 51 Eridani.

astro-ph.EP↗