Abstract: We present time-series spectroscopy and photometry of Gaia DR2 6097540197980557440, a new deeply-eclipsing hot subdwarf B (sdB) + M dwarf (dM) binary. We discovered this object during the course of the Eclipsing Reflection Effect Binaries from Optical Surveys (EREBOS) project, which aims to find new eclipsing sdB+dM binaries (HW Vir systems) and increase the small sample of studied systems. In addition to the primary eclipse, which is in excess of ~5 magnitudes in the optical, the light curve also shows features typical for other HW Vir binaries such as a secondary eclipse and strong reflection effect from the irradiated, cool companion. The orbital period is 0.127037 d (~3 hr), falling right at the peak of the orbital period distribution of known HW Vir systems. Analysis of our time-series spectroscopy yields a radial velocity semi-amplitude of KsdB=100.0±2.0 km/s, which is amongst the fastest line-of-sight velocities found to date for an HW Vir binary. State-of-the-art atmospheric models that account for deviations from local thermodynamic equilibrium are used to determine the atmospheric parameters of the sdB. Although we cannot claim a unique light curve modeling solution, the best-fitting model has an sdB mass of MsdB=0.47±0.03M⊙ and a companion mass of MdM=0.18±0.01M⊙. The radius of the companion appears to be inflated relative to theoretical mass-radius relationships, consistent with other known HW Vir binaries. Additionally, the M dwarf is one of the most massive found to date amongst this type of binary.

Authors: Kyle A. Corcoran, Brad N. Barlow, Veronika Schaffenroth, Ulrich Heber, *Stephen Walser, Andreas Irgang

Publication Journal: The Astrophysical Journal (ApJ)

Citation: Corcoran, K. A., Barlow, B. N., Schaffenroth, V., et al. 2021a, ApJ, 918, 28

Abstract: We present analyses of near-infrared spectroscopic data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey for 45 previously confirmed or candidate white dwarf-main-sequence (WDMS) binaries identified by the optical Sloan Digital Sky Survey (SDSS) and LAMOST surveys. Among these 45 systems, we classify three as having red giant primaries in the LAMOST sample and 14 as young stellar object contaminants in the photometrically identified SDSS sample. From among the subsample of 28 systems that we confirm to have MS primaries, we derive and place limits on orbital periods and velocity amplitudes for 14. Seven systems have significant velocity variations that warrant a post-common-envelope (PCE) binary classification, four of which are newly classified, three of which are newly confirmed, and five for which we can derive full orbital parameters. If confirmed, one of these newly discovered systems (2M14544500+4626456) will have the second-longest orbital period reported for a typical compact PCE WDMS binary (P = 15.1 days). In addition to the seven above, we also recover and characterize with APOGEE data the well-known PCE WDMS systems EG UMa and HZ 9. We also investigate the overall metallicity distribution of the WDMS sample, which is a parameter space not often explored for these systems. Of note, we find one system (2M14244053+4929580) to be extremely metal-poor ([Fe/H] = - 1.42) relative to the rest of the near-solar sample. Additionally, the PCE systems in our sample are found to be, on average, higher in metallicity than their wide-binary counterparts, though we caution that with this small number of systems, the sample may not be representative of the overall distribution of WDMS systems.

Authors: Kyle A. Corcoran, Hannah M. Lewis, Borja Anguiano, Steven R. Majewski, Marina Kounkel, Devin J. McDonald, Keivan G. Stassun, Katia Cunha, Verne Smith, Carlos Allende Prieto, Carles Badenes, Nathan De Lee, Christine N. Mazzola, Penélope Longa-Peña, Alexandre Roman-Lopes

Publication Journal: The Astronomical Journal (AJ)

Citation: Corcoran, K. A., Lewis, H. M., Anguiano, B., et al. 2021b, AJ, 161, 143

Abstract: Hot subdwarf stars are mostly stripped red giants that can exhibit photometric variations due to stellar pulsations, eclipses, the reflection effect, ellipsoidal modulation, and Doppler beaming. Detailed studies of their light curves help constrain stellar parameters through asteroseismological analyses or binary light curve modeling and generally improve our capacity to draw a statistically meaningful picture of this enigmatic stage of stellar evolution. From an analysis of Gaia DR2 flux errors, we have identified around 1200 candidate hot subdwarfs with inflated flux errors for their magnitudes - a strong indicator of photometric variability. As a pilot study, we obtained 2-min cadence TESS Cycle 2 observations of 187 candidate hot subdwarfs with anomalous Gaia flux errors. More than 90% of our targets show significant photometric variations in their TESS light curves. Many of the new systems found are cataclysmic variables, but we report the discovery of several new variable hot subdwarfs, including HW Vir binaries, reflection effect systems, pulsating sdBVs stars, and ellipsoidally modulated systems. We determine atmospheric parameters for select systems using follow-up spectroscopy from the 3-m Shane telescope. Finally, we present a Fourier diagnostic plot for classifying binary light curves using the relative amplitudes and phases of their fundamental and harmonic signals in their periodograms. This plot makes it possible to identify certain types of variables efficiently, without directly investigating their light curves, and may assist in the rapid classification of systems observed in large photometric surveys.

Authors: Brad N. Barlow, Kyle A. Corcoran, *Isabelle M. Parker, Thomas Kupfer, Péter Németh, J. J. Hermes, Isaac D. Lopez, *Will J. Frondorf, *David Vestal, Jazzmyn Holden

Publication Journal: The Astrophysical Journal (ApJ)

Citation: Barlow, B. N., Corcoran, K. A., Parker, I. M., et al. 2022, ApJ, 928, 20

Abstract: We present a novel method to detect variable astrophysical objects and transient phenomena using anomalous excess scatter in repeated measurements from public catalogs of Gaia DR2 and Zwicky Transient Facility (ZTF) DR3 photometry. We first provide a generalized, all-sky proxy for variability using only Gaia DR2 photometry, calibrated to white dwarf stars. To ensure more robust candidate detection, we further employ a method combining Gaia with ZTF photometry and alerts. To demonstrate its efficacy, we apply this latter technique to a sample of roughly 12,100 white dwarfs within 200 pc centered on the ZZ Ceti instability strip, where hydrogen-atmosphere white dwarfs are known to pulsate. By inspecting the top 1% of the samples ranked by these methods, we demonstrate that both the Gaia-only and ZTF-informed techniques are highly effective at identifying known and new variable white dwarfs, which we verify using follow-up, high-speed photometry. We confirm variability in all 33 out of 33 (100%) observed white dwarfs within our top 1% highest-ranked candidates, both inside and outside the ZZ Ceti instability strip. In addition to dozens of new pulsating white dwarfs, we also identify five white dwarfs highly likely to show transiting planetary debris; if confirmed, these systems would more than triple the number of white dwarfs known to host transiting debris.

Authors: Joseph A. Guidry, Zachary P. Vanderbosch, J. J. Hermes, Brad N. Barlow, Isaac D. Lopez, Thomas M. Boudreaux, Kyle A. Corcoran, Keaton J. Bell, Michael H. Montgomery, Tyler M. Heintz, Barbara G. Castanheira, Joshua S. Reding, Bart H. Dunlap, Donald E. Winget, Karen I. Winget, John W. Kuehne

Publication Journal: The Astrophysical Journal (ApJ)

Citation: Guidry, J. A., Vanderbosch, Z. P., Hermes, J. J., et al. 2021, ApJ, 912, 125

Abstract: We present the discovery of EVR-CB-004, a close binary with a remnant stellar core and an unseen white dwarf (WD) companion. The analysis in this work reveals that the primary is potentially an inflated hot subdwarf (sdO) and more likely is a rarer post-blue horizontal branch (post-BHB) star. Post-BHBs are the short-lived shell-burning final stage of a blue horizontal star or hot subdwarf before transitioning to a WD. This object was discovered using Evryscope photometric data in a southern all-sky hot subdwarf variability survey. The photometric light curve for EVR-CB-004 shows multicomponent variability from ellipsoidal deformation of the primary and Doppler boosting, as well as gravitational limb darkening. The binary EVR-CB-004 is one of just a handful of known systems and has a long period (6.08426 hr) and large-amplitude ellipsoidal modulation (16.0% change in brightness from maximum to minimum) for these extremely close binary systems, while the properties of the primary make it a truly unique system. It also shows a peculiar low-amplitude (less than 1%) sinusoidal light-curve variation with a period that is a 1/3 resonance of the binary period. We tentatively identify this additional variation source as a tidally induced resonant pulsation, and we suggest follow-up observations that could verify this interpretation. From the evolutionary state of the system, its components, and its mass fraction, EVR-CB-004 is a strong merger candidate to form a single high-mass (~1.2 M⊙) WD. It offers a glimpse into a brief phase of remnant core evolution and secondary variation not seen before in a compact binary.

Authors: Jeffrey K. Ratzloff, Thomas Kupfer, Brad N. Barlow, David Schneider, Thomas R. Marsh, Ulrich Heber, Kyle A. Corcoran, Evan Bauer, Steven Hämmerich, Henry T. Corbett, Amy Glazier, Ward S. Howard, Nicholas M. Law

Publication Journal: The Astrophysical Journal (ApJ)

Citation: Ratzloff, J. K., Kupfer, T., Barlow, B. N., et al. 2020, ApJ, 902, 92

Abstract: We present EVR-CB-001, the discovery of a compact binary with an extremely low-mass (0.21±0.05M⊙) helium core white dwarf progenitor (pre-He WD) and an unseen low-mass (0.32±0.06M⊙) helium white dwarf (He WD) companion. He WDs are thought to evolve from the remnant helium-rich core of a main-sequence star stripped during the giant phase by a close companion. Low-mass He WDs are exotic objects (only about 0.2% of WDs are thought to be less than 0.3 M⊙), and are expected to be found in compact binaries. Pre-He WDs are even rarer, and occupy the intermediate phase after the core is stripped, but before the star becomes a fully degenerate WD and with a larger radius (≈0.2R⊙) than a typical WD. The primary component of EVR-CB-001 (the pre-He WD) was originally thought to be a hot subdwarf (sdB) star from its blue color and under-luminous magnitude, characteristic of sdBs. The mass, temperature (Teff = 18,500±500 K), and surface gravity (log(g) = 4.96±0.04) solutions from this work are lower than values for typical hot subdwarfs. The primary is likely to be a post-red-giant branch, pre-He WD contracting into a He WD, and at a stage that places it nearest to sdBs on color-magnitude and Teff-log(g) diagrams. EVR-CB-001 is expected to evolve into a fully double degenerate, compact system that should spin down and potentially evolve into a single hot subdwarf star. Single hot subdwarfs are observed, but progenitor systems have been elusive.

Authors: Jeffrey K. Ratzloff, Brad N. Barlow,Thomas Kupfer, Kyle A. Corcoran, Stephan Geier, Evan Bauer, Henry T. Corbett, Ward S. Howard, Amy Glazier, Nicholas M. Law

Publication Journal: The Astrophysical Journal (ApJ)

Citation: Ratzloff, J. K., Barlow, B. N., Kupfer, T., et al. 2019b, ApJ, 883, 51

Abstract: We performed radio searches for the "spider" millisecond pulsar (MSP) candidates 4FGL J0935.3+0901, 4FGL J1627.7+3219, and 4FGL J2212.4+0708 using the Green Bank Telescope in an attempt to detect the proposed radio counterpart of the multi-wavelength variability seen in each system. We observed using the VEGAS spectrometer, centered predominantly at 2165 MHz; however, we were also granted observations at 820 MHz for 4FGL J1627.7+3219. We performed acceleration searches on each dataset using PRESTO as well as additional jerk searches of select observations. We see no evidence of a radio counterpart in any of the observations for each of the three systems at this time. Additional observations, perhaps at different orbital phases (e.g., inferior conjunction), may yield detections of an MSP in the future. Therefore, we urge continued monitoring of these systems to fully characterize the radio nature, however faint or variable, of each system.

Authors: Kyle A. Corcoran, Scott M. Ransom, Ryan S. Lynch

Publication Journal: Research Notes of the AAS (RNAAS)

Citation: Corcoran, K. A., Ransom, S. M., & Lynch, R. S.,  RNAAS, 7, 41

Abstract: We have created a new and unique database, the APOGEE-Galaxy Evolution Explorer (GALEX)-Gaia catalog, to study white dwarfs in close binaries, and, in particular, to: (1) create a minimally biased sample of white dwarf-main sequence (WDMS) systems derived from the combination of GALEX, Gaia, and the dual hemisphere, multi-epoch, high-resolution, infrared APOGEE-1 and -2 spectroscopic surveys, and (2) exploit this catalog to vastly increase the number of well-characterized WDMS systems having derived dynamical parameters (e.g., masses, separation, orbital periods, etc.) as well as precision multi-element chemical compositions by exploiting the high resolution, multi-epoch data from APOGEE. This catalog will significantly further our understanding of compact binary evolution.

Authors: Borja Anguiano, Hannah M. Lewis, Kyle A. Corcoran, Jasmin Washington, Steven R. Majewski, Carlos Allende Prieto, Christine N. Mazzola, Carles Badenes, Keivan G. Stassun, John Blondin

Publication Journal: Research Notes of the American Astronomical Society (RNAAS)

Citation: Anguiano, B., et al. 2021, RNAAS, 4, 127

Abstract: The digital age has sparked a revival in the use of "dark mode" (DM) design in many everyday applications as well as text editors and integrated developer environments. We present the case for adding a DM theme to astronomical journals, including a modified class file that generates the theme you see here as a potential option. DM themes have many beneficial attributes to a user such as saving battery power and reducing screen burn-in on devices with OLED screens, increasing figure hopping efficiency, pairing well with colorblind-friendly palettes, and limiting rhodopsin loss while observing. We analyzed iPoster design trends from AAS 237 and 238 to gauge the possible reception of our DM theme, and we estimate that at least 35%, but likely closer to 42%, of the community would welcome this addition to journals. There are some drawbacks to using a DM theme when reading papers, including increased ink usage when reading in a print medium and some diminished legibility and comprehension in low-light conditions. While these issues are not negligible, we believe they can be mitigated, especially with a paired submission of both a DM and traditional, "light mode" manuscript. It is also likely that many of us will become better astronomers as a result of adding DM to journals.

Authors: Kyle A. Corcoran & Ellorie M. Corcoran

Year: 2022