The B-emission line stars are rapid rotators that were probably spun up by mass and angular momentum accretion through mass transfer in an interacting binary. Mass transfer will strip the donor star ...of its envelope to create a small and hot subdwarf remnant. Here we report on Hubble Space Telescope/STIS far-ultraviolet spectroscopy of a sample of Be stars that reveals the presence of the hot sdO companion through the calculation of cross-correlation functions of the observed and model spectra. We clearly detect the spectral signature of the sdO star in 10 of the 13 stars in the sample, and the spectral signals indicate that the sdO stars are hot, relatively faint, and slowly rotating as predicted by models. A comparison of their temperatures and radii with evolutionary tracks indicates that the sdO stars occupy the relatively long-lived, He-core burning stage. Only one of the ten detections was a known binary prior to this investigation, which emphasizes the difficulty of finding such Be+sdO binaries through optical spectroscopy. However, these results and others indicate that many Be stars probably host hot subdwarf companions.
Starting in 2008, NASA has provided the exoplanet community an observational program aimed at obtaining the highest resolution imaging available as part of its mission to validate and characterize ...exoplanets, as well as their stellar environments, in search of life in the universe. Our current program uses speckle interferometry in the optical (320-1000 nm) with new instruments on the 3.5-m WIYN and both 8-m Gemini telescopes. Starting with Kepler and K2 follow-up, we now support TESS and other space- and ground-based exoplanet related discovery and characterization projects. The importance of high-resolution imaging for exoplanet research comes via identification of nearby stellar companions that can dilute the transit signal and confound derived exoplanet and stellar parameters. Our observations therefore provide crucial information allowing accurate planet and stellar properties to be determined. Our community program obtains high-resolution imagery, reduces the data, and provides all final data products, without any exclusive use period, to the community via the Exoplanet Follow-Up Observation Program (ExoFOP) website maintained by the NASA Exoplanet Science Institute. This paper describes the need for high-resolution imaging and gives details of the speckle imaging program, highlighting some of the major scientific discoveries made along the way.
Rapid rotation in massive stars imposes a latitudinal variation in the mass loss from radiatively driven winds that can lead to enhanced mass loss at the poles (with little angular momentum loss) ...and/or equator (with maximal angular momentum loss). Here we present an examination of the stellar wind lines of the two O-type stars with the fastest known equatorial velocities, VFTS 102 (\(V\sin i = 610 \pm 30\) km/s; O9:Vnnne+) and VFTS 285 (\(V\sin i = 609 \pm 29\) km/s; O7.5 Vnnn) in the Large Magellanic Cloud. Ultraviolet spectra of both stars were obtained with the Hubble Space Telescope Cosmic Origins Spectrograph. The spectrum of VFTS 285 displays a fast outflow in N V and a much slower wind in Si IV, and we argue that there is a two-wind regime in which mass loss is strong at the poles (fast and tenuous wind) but dominant at the equator (slow and dense winds). These ions and wind lines are not present in the spectrum of the cooler star VFTS 102, but the double-peaked H\(\alpha\) emission in its spectrum implies equatorial mass loss into a circumstellar disk. The results suggest that in the fastest rotating O-stars, most mass is lost as an equatorial outflow, promoting angular momentum loss that contributes to a spin down over time.
Hot Jupiters were many of the first exoplanets discovered in the 1990s, but in the decades since their discovery, the mysteries surrounding their origins remain. Here, we present nine new hot ...Jupiters (TOI-1855 b, TOI-2107 b, TOI-2368 b, TOI-3321 b, TOI-3894 b, TOI-3919 b, TOI-4153 b, TOI-5232 b, and TOI-5301 b) discovered by NASA's TESS mission and confirmed using ground-based imaging and spectroscopy. These discoveries are the first in a series of papers named the Migration and Evolution of giant ExoPlanets (MEEP) survey and are part of an ongoing effort to build a complete sample of hot Jupiters orbiting FGK stars, with a limiting Gaia \(G\)-band magnitude of 12.5. This effort aims to use homogeneous detection and analysis techniques to generate a set of precisely measured stellar and planetary properties that is ripe for statistical analysis. The nine planets presented in this work occupy a range of masses (0.55 Jupiter masses (M\(_{\rm{J}}\)) \(<\) M\(_{\rm{P}}\) \(<\) 3.88 M\(_{\rm{J}}\)) and sizes (0.967 Jupiter radii (R\(_{\rm{J}}\)) \(<\) R\(_{\rm{P}}\) \(<\) 1.438 R\(_{\rm{J}}\)) and orbit stars that range in temperature from 5360 K \(<\) Teff \(<\) 6860 K with Gaia \(G\)-band magnitudes ranging from 11.1 to 12.7. Two of the planets in our sample have detectable orbital eccentricity: TOI-3919 b (\(e = 0.259^{+0.033}_{-0.036}\)) and TOI-5301 b (\(e = 0.33^{+0.11}_{-0.10}\)). These eccentric planets join a growing sample of eccentric hot Jupiters that are consistent with high-eccentricity tidal migration, one of the three most prominent theories explaining hot Jupiter formation and evolution.
Mass transfer in an interacting binary will often strip the mass donor of its entire envelope and spin up the mass gainer to near critical rotation. The nearby B-type star Regulus represents a binary ...in the post-mass transfer stage: it is a rapid rotator with a very faint companion in a 40 d orbit. Here we present the results of a search for the spectral features of the stripped-down star in an extensive set of high S/N and high resolution spectra obtained with the CFHT/ESPaDOnS and TBL/NARVAL spectrographs. We first determine revised orbital elements in order to set accurate estimates of the orbital Doppler shifts at the times of observation. We then calculate cross-correlation functions of the observed and model spectra, and we search for evidence of the companion signal in the residuals after removal of the strong primary component. We detect a weak peak in the co-added residuals that has the properties expected for a faint pre-white dwarf. We use the dependence of the peak height and width on assumed secondary velocity semiamplitude to derive the semiamplitude, which yields masses of \(M_1/M_\odot = 3.7 \pm 1.4\) and \(M_2/M_\odot = 0.31 \pm 0.10\) (assuming orbital inclination equals the spin inclination of Regulus). We estimate the pre-white dwarf temperature \(T_{\rm eff} = (20 \pm 4)\)~kK through tests with differing temperature model spectra, and we find the radius \(R_2/R_\odot = 0.061 \pm 0.011\) from the component temperatures and the flux ratio associated with the amplitude of the signal in the cross-correlation residuals.
We present high angular resolution imaging observations of 517 host stars of TESS exoplanet candidates using the `Alopeke and Zorro speckle cameras at Gemini North and South. The sample consists ...mainly of bright F, G, K stars at distances of less than 500 pc. Our speckle observations span angular resolutions of ~20 mas out to 1.2 arcsec, yielding spatial resolutions of <10 to 500 AU for most stars, and our contrast limits can detect companion stars 5-9 magnitudes fainter than the primary at optical wavelengths. We detect 102 close stellar companions and determine the separation, magnitude difference, mass ratio, and estimated orbital period for each system. Our observations of exoplanet host star binaries reveal that they have wider separations than field binaries, with a mean orbital semi-major axis near 100 AU. Other imaging studies have suggested this dearth of very closely separated binaries in systems which host exoplanets, but incompleteness at small separations makes it difficult to disentangle unobserved companions from a true lack of companions. With our improved angular resolution and sensitivity, we confirm that this lack of close exoplanet host binaries is indeed real. We also search for a correlation between planetary orbital radii vs. binary star separation, but given the very short orbital periods of the TESS planets, we do not find any clear trend. We do note that in exoplanet systems containing binary host stars, there is an observational bias against detecting Earth-size planet transits due to transit depth dilution caused by the companion star.
We present a photometric and light curve analysis of an eccentric eclipsing binary in the K2 Campaign 0 field that resides in Sh 2-252E, a young star cluster embedded in an H II region. We describe a ...spectroscopic investigation of the three brightest stars in the crowded aperture to identify which is the binary system. We find that none of these stars are components of the eclipsing binary system, which must be one of the fainter nearby stars. These bright cluster members all have remarkable spectra: Sh 2-252a (EPIC 202062176) is a B0.5 V star with razor sharp absorption lines, Sh 2-252b is a Herbig A0 star with disk-like emission lines, and Sh 2-252c is a pre-main sequence star with very red color.
With data from the Transiting Exoplanet Survey Satellite (TESS), we showcase improvements to the MIT Quick-Look Pipeline (QLP) through the discovery and validation of a multi-planet system around ...M-dwarf TOI 4342 (\(T_{mag}=11.032\), \(M_* = 0.63 M_\odot\), \(R_* = 0.60 R_\odot\), \(T_{eff} = 3900\) K, \(d = 61.54\) pc). With updates to QLP, including a new multi-planet search, as well as faster cadence data from TESS' First Extended Mission, we discovered two sub-Neptunes (\(R_b = 2.266_{-0.038}^{+0.038} R_\oplus\) and \(R_c = 2.415_{-0.040}^{+0.043} R_\oplus\); \(P_b\) = 5.538 days and \(P_c\) = 10.689 days) and validated them with ground-based photometry, spectra, and speckle imaging. Both planets notably have high transmission spectroscopy metrics (TSMs) of 36 and 32, making TOI 4342 one of the best systems for comparative atmospheric studies. This system demonstrates how improvements to QLP, along with faster cadence Full-Frame Images (FFIs), can lead to the discovery of new multi-planet systems.
We report the Transiting Exoplanet Survey Satellite (TESS) discovery of a three-planet system around the bright Sun-like star HD~22946(V=8.3 mag),also known as TIC~100990000, located 63 parsecs ...away.The system was observed by TESS in Sectors 3, 4, 30 and 31 and two planet candidates, labelled TESS Objects of Interest (TOIs) 411.01 (planet \(c\)) and 411.02 (planet \(b\)), were identified on orbits of 9.57 and 4.04 days, respectively. In this work, we validate the two planets and recover an additional single transit-like signal in the light curve, which suggests the presence of a third transiting planet with a longer period of about 46 days.We assess the veracity of the TESS transit signals and use follow-up imaging and time series photometry to rule out false positive scenarios, including unresolved binary systems, nearby eclipsing binaries or background/foreground stars contaminating the light curves. Parallax measurements from Gaia EDR3, together with broad-band photometry and spectroscopic follow-up by TFOP allowed us to constrain the stellar parameters of TOI-411, including its radius of\(1.157\pm0.025R_\odot\). Adopting this value, we determined the radii for the three exoplanet candidates and found that planet \(b\) is a super-Earth, with a radius of \(1.72\pm0.10R_\oplus\), while planet \(c\) and \(d\) are sub-Neptunian planets, with radii of\(2.74\pm0.14R_\oplus\) and \(3.23\pm0.19R_\oplus\) respectively. By using dynamical simulations, we assessed the stability of the system and evaluated the possibility of the presence of other undetected, non-transiting planets by investigating its dynamical packing. We find that the system is dynamically stable and potentially unpacked, with enough space to host at least one more planet between \(c\) and \(d\).(Abridged)
