[en] The field of asteroseismology has enjoyed a large swath of data coming from recent missions (e.g., CoRoT, Kepler, K2). This wealth of new data has allowed the field to expand beyond the previous limitation of a few extremely bright and evolved stars. Asteroseismology relies on accurate surface measurements for boundary conditions, but the predicted physical parameters in the Kepler Input Catalog (KIC) are unreliable for hot stars. We present stellar parameters of 25 candidate pulsating B-star candidates in the Kepler field. We use blue optical spectra to measure the projected rotational velocity ($V\sin <!--\; ???\; -->i$), effective temperature (T _eff), and surface gravity ($\mathrm{l}\mathrm{o}\mathrm{g}g$) using TLUSTY and Kurucz ATLAS9 model atmospheres. We find a large discrepancy between our spectroscopically derived parameters and those derived from photometry in the KIC and Gaia Data Release 2 (DR2). Using spectral energy distributions, we also measure the radii of these stars and later calculate the luminosities and masses. We find the extinctions (A _V) of these stars to be consistent with zero, which is expected for stars of high Galactic latitude.

[en] Be stars have generally been characterized by the emission lines in their spectra, and especially the time variability of those spectroscopic features. They are known to also exhibit photometric variability at multiple timescales, but have not been broadly compared and analyzed by that behavior. We have taken advantage of the advent of wide-field, long-baseline, and high-cadence photometric surveys that search for transiting exoplanets to perform a comprehensive analysis of brightness variations among a large number of known Be stars. The photometric data comes from the KELT transit survey, with a typical cadence of 30 minutes, a baseline of up to 10 years, photometric precision of about 1%, and coverage of about 60% of the sky. We analyze KELT light curves of 610 known Be stars in both the northern and southern hemispheres in an effort to study their variability. Consistent with other studies of Be star variability, we find most of the stars to be photometrically variable. We derive lower limits on the fraction of stars in our sample that exhibit features consistent with non-radial pulsations (25%), outbursts (36%), and long-term trends in the circumstellar disk (37%), and show how these are correlated with spectral sub-types. Other types of variability, such as those owing to binarity, are also explored. Simultaneous spectroscopy for some of these systems from the Be Star Spectra database allow us to better understand the physical causes for the observed variability, especially in cases of outbursts and changes in the disk.

[en] Prompted by X-ray detections from multiple surveys, we investigated the A-type star HD 63021 and found that it is a double-lined spectroscopic binary with highly variable emission associated with the primary star. Analysis of our multiepoch spectroscopic observations, the majority of which were carried out on small-aperture telescopes, indicates a very short orbital period of just 2.9 days and a mass ratio M ₂/M ₁ of 0.23. The A1 V star is a slow rotator, with a rotational speed of ∼34 km s⁻¹. Assuming that its mass is 2.3 M _⊙, the present-day secondary is an evolved star of ∼0.5 M _⊙ that nearly fills its Roche lobe. This secondary star rotates comparatively rapidly at ∼44 km s⁻¹, and we see evidence that it is chromospherically active. Analysis of a photometric light curve from TESS reveals two strong periods, one at the orbital period for the system and another at half the orbital period. These findings suggest that HD 63021 is a close binary system undergoing mass transfer from the secondary star onto the primary star—in all ways like an Algol eclipsing binary system, except without the eclipse. We discuss the system’s mass transfer, which is not steady but seems to run in fits and bursts, and infer the system’s basic physical properties from an orbital parameter study, the Roche lobe geometry, and its extant X-ray emission.

[en] We present the discovery of a hot Jupiter transiting the V = 9.23 mag main-sequence A-star KELT-17 (BD+14 1881). KELT-17b is a ${1.31}_{-<!--\; ???\; -->0.29}^{+0.28}{M}_{\mathrm{J}}$, ${1.525}_{-<!--\; ???\; -->0.060}^{+0.065}{R}_{\mathrm{J}}$ hot-Jupiter in a 3.08-day period orbit misaligned at −115.°9 ± 4.°1 to the rotation axis of the star. The planet is confirmed via both the detection of the radial velocity orbit, and the Doppler tomographic detection of the shadow of the planet during two transits. The nature of the spin–orbit misaligned transit geometry allows us to place a constraint on the level of differential rotation in the host star; we find that KELT-17 is consistent with both rigid-body rotation and solar differential rotation rates ($\mathrm{\alpha <!--\; ??\; -->}<<!--\; <\; -->0.30$ at $2\mathrm{\sigma <!--\; ??\; -->}$ significance). KELT-17 is only the fourth A-star with a confirmed transiting planet, and with a mass of ${1.635}_{-<!--\; ???\; -->0.061}^{+0.066}{M}_{\odot <!--\; ???\; -->}$, an effective temperature of 7454 ± 49 K, and a projected rotational velocity of $v\sin I_{\ast <!--\; ???\; -->}={44.2}_{-<!--\; ???\; -->1.3}^{+1.5}\mathrm{k}\mathrm{m}{\mathrm{s}}^{-<!--\; ???\; -->1};$ it is among the most massive, hottest, and most rapidly rotating of known planet hosts.

[en] We report on the H -band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These “snapshots” of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance of the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.

[en] We report the discovery of KELT J041621-620046, a moderately bright (J ∼ 10.2) M-dwarf eclipsing binary system at a distance of 39 ± 3 pc. KELT J041621-620046 was first identified as an eclipsing binary using observations from the Kilodegree Extremely Little Telescope (KELT) survey. The system has a short orbital period of ∼1.11 days and consists of components with $M_1={0.447}_{+0.052}^{-<!--\; ???\; -->0.047}{M}_{\odot <!--\; ???\; -->}$ and $M_2={0.399}_{+0.046}^{-<!--\; ???\; -->0.042}{M}_{\odot <!--\; ???\; -->}$ in nearly circular orbits. The radii of the two stars are $R_1={0.540}_{+0.034}^{-<!--\; ???\; -->0.032}{R}_{\odot <!--\; ???\; -->}$ and $R_2=0.453\pm <!--\; ??\; -->0.017R_{\odot <!--\; ???\; -->}$. Full system and orbital properties were determined (to ∼10% error) by conducting an EBOP (Eclipsing Binary Orbit Program) global modeling of the high precision photometric and spectroscopic observations obtained by the KELT Follow-up Network. Each star is larger by 17%–28% and cooler by 4%–10% than predicted by standard (non-magnetic) stellar models. Strong Hα emission indicates chromospheric activity in both stars. The observed radii and temperature discrepancies for both components are more consistent with those predicted by empirical relations that account for convective suppression due to magnetic activity.

[en] We present the discoveries of KELT-25 b (TIC 65412605, TOI-626.01) and KELT-26 b (TIC 160708862, TOI-1337.01), two transiting companions orbiting relatively bright, early A stars. The transit signals were initially detected by the KELT survey and subsequently confirmed by Transiting Exoplanet Survey Satellite (TESS) photometry. KELT-25 b is on a 4.40 day orbit around the V = 9.66 star CD-24 5016 ($T_{\mathrm{e}\mathrm{f}\mathrm{f}}={8280}_{-<!--\; ???\; -->180}^{+440}$ K, M_⋆ = ${2.18}_{-<!--\; ???\; -->0.11}^{+0.12}$ M_⊙), while KELT-26 b is on a 3.34 day orbit around the V = 9.95 star HD 134004 ($T_{\mathrm{e}\mathrm{f}\mathrm{f}}$ = ${8640}_{-<!--\; ???\; -->240}^{+500}$ K, M_⋆ = ${1.93}_{-<!--\; ???\; -->0.16}^{+0.14}$ M_⊙), which is likely an Am star. We have confirmed the substellar nature of both companions through detailed characterization of each system using ground-based and TESS photometry, radial velocity measurements, Doppler tomography, and high-resolution imaging. For KELT-25, we determine a companion radius of R_P = ${1.64}_{-<!--\; ???\; -->0.043}^{+0.039}$ R_J and a 3σ upper limit on the companion’s mass of ∼64 M_J. For KELT-26 b, we infer a planetary mass and radius of M_P = ${1.41}_{-<!--\; ???\; -->0.51}^{+0.43}$ $M_{\mathrm{J}}$ and R_P = ${1.94}_{-<!--\; ???\; -->0.058}^{+0.060}$ R_J. From Doppler tomographic observations, we find KELT-26 b to reside in a highly misaligned orbit. This conclusion is weakly corroborated by a subtle asymmetry in the transit light curve from the TESS data. KELT-25 b appears to be in a well-aligned, prograde orbit, and the system is likely a member of the cluster Theia 449.