The Transiting Exoplanet Survey Satellite (TESS) is finding transiting planet candidates around bright, nearby stars across the entire sky. The large field of view, however, results in low spatial resolution; therefore, multiple stars contribute to almost every TESS light curve. High angular resolution imaging can detect the previously unknown companions to planetary candidate hosts that dilute the transit depths, lead to host star ambiguity, and, in some cases, are the source of false-positive transit signals. We use speckle imaging on the Southern Astrophysical Research (SOAR) telescope to search for companions to 542 TESS planet candidate hosts in the southern sky. We provide correction factors for the 117 systems with resolved companions due to photometric contamination. The contamination in TESS due to close binaries is similar to that found in surveys of Kepler planet candidates. For the solar-type population, we find a deep deficit of close binary systems with projected stellar separations less than 100 au among planet candidate hosts (44 observed binaries compared to 124 expected based on field binary statistics). The close binary suppression among TESS planet candidate hosts is similar to that seen for the more distant Kepler population. We also find a large surplus of TESS planet candidates in wide binary systems detected in both SOAR and Gaia DR2 (Cat. I/345) (119 observed binaries compared to 77 expected). These wide binaries almost exclusively host giant planets, however, suggesting that orbital migration caused by perturbations from the stellar companion may lead to planet-planet scattering and suppress the population of small planets in wide binaries. Both trends are also apparent in the M dwarf planet candidate hosts.
We present an overview and first results of the Stratospheric Observatory For Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the FORCAST instrument to image massive protostars from ~10 to 40{mu}m. These wavelengths trace thermal emission from warm dust, which in Core Accretion models mainly emerges from the inner regions of protostellar outflow cavities. Dust in dense core envelopes also imprints characteristic extinction patterns at these wavelengths, causing intensity peaks to shift along the outflow axis and profiles to become more symmetric at longer wavelengths. We present observational results for the first eight protostars in the survey, i.e., multiwavelength images, including some ancillary ground-based mid- infrared (MIR) observations and archival Spitzer and Herschel data. These images generally show extended MIR/FIR emission along directions consistent with those of known outflows and with shorter wavelength peak flux positions displaced from the protostar along the blueshifted, near-facing sides, thus confirming qualitative predictions of Core Accretion models. We then compile spectral energy distributions and use these to derive protostellar properties by fitting theoretical radiative transfer models. Zhang and Tan models, based on the Turbulent Core Model of McKee and Tan, imply the sources have protostellar masses m*~10-50M_{sun}_ accreting at ~10^-4^-10^-3^M_{sun}_/yr inside cores of initial masses Mc~30-500M_{sun}_ embedded in clumps with mass surface densities {Sigma}_cl_~0.1-3g/cm^2^. Fitting the Robitaille et al. models typically leads to slightly higher protostellar masses, but with disk accretion rates ~100x smaller. We discuss reasons for these differences and overall implications of these first survey results for massive star formation theories.
We present basic observational data and association membership analysis for 45 young and active low-mass stellar systems from the ongoing Research Consortium On Nearby Stars photometry and astrometry program at the Cerro Tololo Inter-American Observatory. Most of these systems have saturated X-ray emission (log(L_X_/L_bol_)>-3.5) based on X-ray fluxes from the ROSAT All-Sky Survey, and many are significantly more luminous than main-sequence stars of comparable color. We present parallaxes and proper motions, Johnson-Kron-Cousins VRI photometry, and multiplicity observations from the CTIOPI program on the CTIO 0.9m telescope. To this we add low-resolution optical spectroscopy and line measurements from the CTIO 1.5m telescope, and interferometric binary measurements from the Hubble Space Telescope Fine Guidance Sensors. We also incorporate data from published sources: JHK_S_ photometry from the Two Micron All Sky Survey point source catalog, X-ray data from the ROSAT All-Sky Survey, and radial velocities from literature sources. Within the sample of 45 systems, we identify 21 candidate low-mass pre-main-sequence members of nearby associations, including members of {beta} Pictoris, TW Hydrae, Argus, AB Doradus, two ambiguous {approx}30Myr old systems, and one object that may be a member of the Ursa Major moving group. Of the 21 candidate young systems, 14 are newly identified as a result of this work, and six of those are within 25pc of the Sun.
We present trigonometric, photometric, and photographic distances to 1748 southern ({delta}{<=}O{deg}) M dwarf systems with {mu}>=0.18''/yr, of which 1404 are believed to lie within 25pc of the Sun. The stars have 6.67{<=}V_J_{<=}21.38 and 3.50{<=}(V_J_-K_S_){<=}9.27, covering the entire M dwarf spectral sequence from M0.0 V through M9.5 V. This sample therefore provides a comprehensive snapshot of our current knowledge of the southern sky for the nearest M dwarfs that dominate the stellar population of the Galaxy. Roughly one-third of the 1748 systems, each of which has an M dwarf primary, have published high quality parallaxes, including 179 from the REsearch Consortium On Nearby Stars astrometry program. For the remaining systems, we offer photometric distance estimates that have well-calibrated errors. The bulk of these (~700) are based on new V_J_R_KC_I_KC_ photometry acquired at the CTIO/SMARTS 0.9m telescope, while the remaining 500 primaries have photographic plate distance estimates calculated using SuperCOSMOS B_J_R_59F_I_IVN_ photometry. Confirmed and candidate subdwarfs in the sample have been identified, and a census of companions is included.
Solar neighborhood XXXVIII. Nearby M dwarf systems
Short Name:
J/AJ/153/14
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 160 new trigonometric parallaxes for 151 M dwarf systems from the REsearch Consortium On Nearby Stars (RECONS) group's long-term astrometry/photometry program at the CTIO/SMARTS 0.9m telescope. Most systems (124 or 82%) are found to lie within 25pc. The stars have 119mas/yr{<=}{mu}{<=}828mas/yr and 3.85{<=}(V-K){<=}8.47. Among these are 58 systems from the SuperCOSMOS-RECONS search, discovered via our proper motion trawls of the SuperCOSMOS digitized archival photographic plates, while the remaining stars were suspected via photometric distance estimates to lie nearby. Sixteen systems were newly discovered via astrometric perturbations to be binaries, many of which are ideal for accurate mass determinations due to their proximity and orbital periods on the order of a decade. A variability analysis of the stars presented, two-thirds of which are new results, shows six of the stars to vary by more than 20mmag. This effort brings the total number of parallaxes for M dwarf systems measured by RECONS to nearly 500 and increases by 26% the number of southern M dwarf systems with accurate trigonometric parallaxes placing them within 25pc.
Using recent photometric calibrations, we develop greatly improved distance estimates for DA white dwarfs using multi-band synthetic photometry based on spectroscopic temperatures and gravities. Very good correlations are shown to exist between our spectroscopically based photometric distance estimates and those derived from trigonometric parallaxes. We investigate the uncertainties involved in our distance estimates, as well as discuss the circumstances where such techniques are most likely to fail. We apply our techniques to the large sample of Sloan Digital Sky Survey DA white dwarfs where automated fitting of HI Balmer profiles yields spectrometric temperatures and gravities. We determine simple empirical corrections to these temperatures and gravities with respect to published slit spectroscopy. After applying these T_eff_-logg corrections as well as appropriate interstellar extinction corrections, where necessary, we derive spectroscopically based photometric distances for 7062 DA stars from this sample.
We present a near-infrared study of the stellar content of 35 HII regions in the Galactic plane, 24 of which have been classified as giant H ii regions. We have selected these optically obscured star-forming regions from the catalogues of Russeil (2003, Cat. J/A+A/397/133), Conti & Crowther (2004MNRAS.355..899C) and Bica et al. (2003, Cat. J/A+A/404/223). In this paper, we have used the near-infrared domain J-, H- and Ks-band colour images to visually inspect the sample. Also, we have used colour-colour and colour-magnitude diagrams to indicate ionizing star candidates, as well as the presence of young stellar objects such as classical T Tauri stars and massive young stellar objects (MYSOs). We have obtained Spitzer Infrared Array Camera images for each region to help further characterize them. Spitzer and near-infrared morphology were used to place each cluster in an evolutionary phase of development. Spitzer photometry was also used to classify the MYSOs.
We present a detailed spectroscopic and photometric analysis of 219 DA and DB white dwarfs for which trigonometric parallax measurements are available. Our aim is to compare the physical parameters derived from the spectroscopic and photometric techniques, and then to test the theoretical mass-radius relation for white dwarfs using these results. The agreement between spectroscopic and photometric parameters is found to be excellent, especially for effective temperatures, showing that our model atmospheres and fitting procedures provide an accurate, internally consistent analysis. The values of surface gravity and solid angle obtained, respectively, from spectroscopy and photometry, are combined with parallax measurements in various ways to study the validity of the mass-radius relation from an empirical point of view. After a thorough examination of our results, we find that 73% and 92% of the white dwarfs are consistent within 1{sigma} and 2{sigma} confidence levels, respectively, with the predictions of the mass-radius relation, thus providing strong support to the theory of stellar degeneracy. Our analysis also allows us to identify 15 stars that are better interpreted in terms of unresolved double degenerate binaries. Atmospheric parameters for both components in these binary systems are obtained using a novel approach. We further identify a few white dwarfs that are possibly composed of an iron core rather than a carbon/oxygen core, since they are consistent with Fe-core evolutionary models.
Distance estimates based on low-resolution spectroscopy and Two Micron All Sky Survey (2MASS, Cat. <II/246>) J magnitudes are presented for 322 nearby candidates from Luyten's NLTT catalogue (<I/98>). Mainly relatively bright (typically 7<Ks<11) and red high proper motion stars have been selected according to their 2MASS magnitudes and optical-to-infrared colours (+1<R-Ks<+7). Some LHS stars previously lacking spectroscopy have also been included. We have classified the majority of the objects as early-M dwarfs (M2-M5). More than 70% of our targets turned out to lie within the 25pc horizon of the catalogue of nearby stars, with 50 objects placed within 15pc and 8 objects being closer than 10pc. Three objects in the 10pc sample have no previously published spectral type: LP 876-10 (M4), LP 870-65 (M4.5), and LP 869-26 (M5). A large fraction of the objects in our sample (57%) ave independent distance estimates, mainly by the recent efforts of Reid and collaborators. Our distance determinations are generally in good agreement with theirs. 11 rather distant (d>100pc) objects have also been identified, including a probable halo, but relatively hot (Teff=13000K) white dwarf (LHS 1200) and 10 red dwarfs with extremely large tangential velocities (250<v_t_<1150km/s). Altogether, there are 11 red dwarfs (including one within 70pc) with tangential velocities larger than about 250km/s. All these objects are suspected to be in fact subdwarfs, if so, their distances would be only about half of our original estimates. The three most extreme objects in that respect are the K and early M dwarfs LP 323-168, LHS 5343 and LP 552-21 with corrected distances between 180pc and 400pc and resulting tangential velocities still larger than about 400km/s.
We present low-resolution optical spectroscopy and BVRI photometry of 453 candidate nearby stars drawn from the NLTT (<I/98>) proper-motion catalog. The stars were selected based on optical/near-infrared colors, derived by combining the NLTT photographic data with photometry from the 2MASS Second Incremental Data Release (<II/241>). Based on the derived photometric and spectroscopic parallaxes, we identify 111 stars as lying within 20pc of the Sun, including nine stars with formal distance estimates of less than 10pc. A further 53 stars have distance estimates within 1{sigma} of our 20pc limit. Almost all of those stars are additions to the nearby-star census. In total, our NLTT-based survey has so far identified 496 stars likely to be within 20pc, of which 195 are additions to nearby-star catalogs. Most of the newly identified nearby stars have spectral types between M4 and M8.
