arXiv subjects

Catherine Pilachowski

Publications and source records attributed to Catherine Pilachowski.

3 recordsLinked to original sources

arXiv2026

The Composition of M-dwarf Exoplanet Hosts: Atmospheric Parameters and O, Mg, Si, and Fe Abundances from IR Spectroscopy

Determining M-dwarf abundances is an important step to discerning the chemical evolution of the Milky Way and characterizing exoplanetary systems, especially since these objects commonly host small exoplanets. However, a dearth of M-dwarf abundance measurements exist compared to Sun-like stars, partially due to their complicated optical spectra dominated by molecular absorption lines and low luminosities. To overcome these issues, we have obtained high resolution H-band spectra of 40 planet-hosting M-dwarf stars and 2 M-dwarfs in wide binaries with FGK primaries with IGRINS on Gemini South and on the McDonald Observatory 2.7m telescope, and NIRSPEC on Keck. Abundances were derived by comparing each observed spectrum to synthetic spectral grids generated with MOOG and MARCS atmospheric models. Effective temperatures were derived using OH and H$_{2}$O lines and [Fe/H] from Fe I and FeH lines. Both Mg and Si abundances were determined using atomic features. Overall, we find that our abundances are broadly consistent with previous literature M-dwarf abundances. We complemented our abundances analysis with UVW velocities and Milky Way stellar population membership probabilities and identified 2 potential thick disk stars from our kinematic and chemical analysis: GJ 1252 and L181-1 which was a previously known thick disk star. Kinematic stellar population probabilities and a low [Fe/H] abundance makes Kepler 42 a likely thick disk star, although uncertain Mg and Si abundances make classification difficult. Lastly, we have determined Si/Mg and Fe/Mg molar ratios for M-dwarf exoplanet hosts and find the abundance distributions leads to exoplanet core-mass fractions between 20 - 40$\%$.

astro-ph.SR↗

arXiv2024

Transitory tidal heating and its impact on cluster isochrones

The kinetic energy in tidal flows, when converted into heat, can affect the internal structure of a star and shift its location on a color-magnitude diagram from that of standard models. In this paper we explore the impact of injecting heat into stars with masses near the main sequence turnoff mass (1.26 $M_\odot$) of the open cluster M67. The heating rate is obtained from the tidal shear energy dissipation rate which is calculated from first principles by simultaneously solving the equations that describe orbital motion and the response of a star's layers to the gravitational, Coriolis, centrifugal, gas pressure and viscous forces. The stellar structure models are computed with MESA. We focus on the effects of injecting heat in pulses lasting 0.01 Gyr, a timeframe consistent with the synchonization timescale in binary systems. We find that the location of the tidally perturbed stars in the M67 color-magnitude diagram is shifted to significantly higher luminosities and effective temperatures than predicted by the standard model isochrone and include locations corresponding to some of the Blue Straggler Stars. Because tidal heating takes energy from the orbit causing it to shrink, Blue Straggler Stars could be merger or mass-transfer progenitors as well as products of these processes.

astro-ph.GA↗

arXiv2020

The Blanco DECam Bulge Survey. I. The Survey Description and Early Results

The Blanco Dark Energy Camera (DECam) Bulge survey is a Vera Rubin Observatory (LSST) pathfinder imaging survey, spanning $\sim 200$ sq. deg. of the Southern Galactic bulge, $-2^\circ <$b$< -13^\circ$ and $-11^\circ <$l$ < +11^\circ$. We have employed the CTIO-4m telescope and the Dark Energy Camera (DECam) to image a contiguous $\sim 200$ sq. deg. region of the relatively less reddened Southern Galactic bulge, in SDSS $u$ + Pan-STARRS$grizy$. Optical photometry with its large colour baseline will be used to investigate the age and metallicity distributions of the major structures of the bulge. Included in the survey footprint are 26 globular clusters imaged in all passbands. Over much of the bulge, we have Gaia DR2 matching astrometry to $i\sim 18$, deep enough to reach the faint end of the red clump. This paper provides the background, scientific case, and description of the survey. We present an array of new reddening-corrected colour-magnitude diagrams that span the extent of Southern Galactic bulge. We argue that a population of massive stars in the blue loop evolutionary phase, proposed to lie in the bulge, are instead at $\sim 2$ kpc from the Sun and likely red clump giants in the old disk. A bright red clump near $(l,b)=(+8^\circ,-4^\circ)$ may be a feature in the foreground disk, or related to the long bar reported in earlier work. We also report the first map of the blue horizontal branch population spanning the BDBS field of regard, and our data does not confirm the reality of a number of proposed globular clusters in the bulge.

astro-ph.GA↗