We describe the catalogs assembled and the algorithms used to populate the revised TESS Input Catalog (TIC), based on the incorporation of the Gaia second data release. We also describe a revised ...ranking system for prioritizing stars for 2 minute cadence observations, and we assemble a revised Candidate Target List (CTL) using that ranking. The TIC is available on the Mikulski Archive for Space Telescopes server, and an enhanced CTL is available through the Filtergraph data visualization portal system at http://filtergraph.vanderbilt.edu/tess_ctl.
ABSTRACT
We examine parallaxes and distances for Galactic luminous blue variables (LBVs) in the Gaia second data release (DR2). The sample includes 11 LBVs and 14 LBV candidates. For about half of ...the sample, DR2 distances are either similar to commonly adopted literature values, or the DR2 values have large uncertainties. For the rest, reliable DR2 distances differ significantly from values in the literature, and in most cases the Gaia DR2 distance is smaller. Two key results are that the S Doradus instability strip may not be as clearly defined as previously thought, and that there exists a population of LBVs at relatively low luminosities. LBVs seem to occupy a wide swath from the end of the main sequence at the blue edge to ∼8000 K at the red side, with a spread in luminosity reaching as low as log(L/L⊙) ≈ 4.5. The lower-luminosity group corresponds to effective single-star initial masses of 10–25 M⊙, and includes objects that have been considered as confirmed LBVs. We discuss implications for LBVs including (1) their instability and origin in binary evolution, (2) connections to some supernova (SN) impostors such as the class of SN 2008S-like objects, and (3) LBVs that may be progenitors of SNe with dense circumstellar material across a wide initial mass range. Although some of the Gaia DR2 distances for LBVs have large uncertainty, this represents the most direct and consistent set of Galactic LBV distance estimates available in the literature.
Abstract
We present the results of the analysis of the photometric data collected in long- and short-cadence mode by the Transiting Exoplanet Survey Satellite for GJ 504, a well-studied ...planet-hosting solar-like star, whose fundamental parameters have been largely debated during the last decade. Several attempts have been made by the present authors to isolate the oscillatory properties expected on this main-sequence star, but we did not find any presence of solar-like pulsations. The suppression of the amplitude of the acoustic modes can be explained by the high level of magnetic activity revealed for this target, not only by the study of the photometric light curve but also by the analysis of three decades of available Mount Wilson spectroscopic data. In particular, our measurements of the stellar rotational period
P
rot
≃ 3.4 days and of the main principal magnetic cycle of ≃12 yr confirm previous findings and allow us to locate this star in the early main-sequence phase of its evolution during which the chromospheric activity is dominated by the superposition of several cycles before the transition to the phase of the magnetic-braking shutdown with the subsequent decrease of the magnetic activity.
The strong mass loss of Luminous Blue Variables (LBVs) is thought to play a critical role in massive-star evolution, but their place in the evolutionary sequence remains debated. A key to ...understanding their peculiar instability is their high observed luminosities, which often depends on uncertain distances. Here we report direct distances and space motions of four canonical Milky Way LBVs-AG Car, HR Car, HD 168607, and (candidate) Hen 3-519-from the Gaia first data release. Whereas the distances of HR Car and HD 168607 are consistent with previous literature estimates within the considerable uncertainties, Hen 3-519 and AG Car, both at ∼2 kpc, are much closer than the 6-8 kpc distances previously assumed. As a result, Hen 3-519 moves far from the locus of LBVs on the Hertzsprung-Russell diagram, making it a much less luminous object. For AG Car, considered a defining example of a classical LBV, its lower luminosity would also move it off the S Dor instability strip. Lower luminosities allow both AG Car and Hen 3-519 to have passed through a previous red supergiant phase, lower the mass estimates for their shell nebulae, and imply that binary evolution is needed to account for their peculiarities. These results may also impact our understanding of LBVs as potential supernova progenitors and their isolated environments. Improved distances will be provided in the Gaia second data release, which will include additional LBVs. AG Car and Hen 3-519 hint that this new information may alter our traditional view of LBVs.
Abstract Our understanding of how exoplanets form and evolve relies on analyses of both the mineralogy of protoplanetary disks and their detailed structures; however, these key complementary aspects ...of disks are usually studied separately. We present initial results from a hybrid model that combines the empirical characterization of the mineralogy of a disk, as determined from its mid-infrared spectral features, with the MCFOST radiative transfer disk model, a combination we call the Empirical and Radiative Transfer Hybrid (EaRTH) Disk Model. With the results of the mineralogy detection serving as input to the radiative transfer model, we generate mid-infrared spectral energy distributions (SEDs) that reflect both the mineralogical and structural parameters of the corresponding disk. Initial fits of the SED output by the resulting integrated model of Spitzer Space Telescope mid-infrared spectra of the protoplanetary disk orbiting the nearby T Tauri star MP Mus demonstrate the potential advantages of this approach by revealing details like the dominance of micron-sized olivine and micron-sized forsterite in this dusty disk. The simultaneous insight into disk composition and structure provided by the EaRTH Disk methodology should be directly applicable to the interpretation of mid-infrared spectra of protoplanetary disks that will be produced by the James Webb Space Telescope.
Abstract
We present second observations by K2 of OJ 287 and seven other
γ
-ray active galactic nuclei (AGNs) obtained in 2017–2018, second and third observations of the lobe-dominated, steep-spectrum ...quasar 3C 207, and observations of nine additional blazars not previously observed with K2. The AGNs were observed simultaneously with K2 and the Fermi Large Area Telescope for 51–81 days. Our full sample, observed in 2014–2018, contained 16 BL Lacertae objects (BL Lacs), nine flat-spectrum radio quasars (FSRQs), and four other
γ
-ray AGNs. Twelve BL Lacs and seven FSRQs exhibited fast, jagged light curves, while four BL Lacs and two FSRQs had slow, smooth light curves. Some objects changed their red-noise character significantly between repeated K2 observations. The optical characteristics of OJ 287 derived from the short-cadence K2 light curves changed between observations made before and after the predicted passage of the suspected secondary supermassive black hole through the accretion disk of the primary supermassive black hole. The average slopes of the periodogram power spectral densities of the BL Lacs’ and FSRQs’ light curves differed significantly, by ≈12%, with the BL Lac slopes being steeper, and a Kolmogorov–Smirnov test with a
p
-value of 0.039 indicates that these samples probably come from different populations; however, this result is not as strongly supported by power spectral response (PSRESP) analyses. Differences in the origin of the jets from the ergosphere or accretion disk in these two classes could produce such a disparity, as could different sizes or locations of emission regions within the jets.
The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Using near-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity ...dispersion of young (1-2 Myr) stars in NGC 1333 is 0.92 + or - 0.12 km s super(-1) after correcting for measurement uncertainties and the effect of binaries. This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion, but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a subvirial velocity dispersion of 0.5 km s super(-1). Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement provides a strong constraint on the initial velocity dispersion of newly formed stars. We propose that the difference in velocity dispersion between stars and dense cores may be due to the influence of a 70 mu G magnetic field acting on the dense cores or be the signature of a cluster with initial substructure undergoing global collapse.
Abstract
We present a catalog of ∼100,000 periodic variable stars in Transiting Exoplanet Survey Satellite (TESS) full-frame image data among members of widely distributed moving groups identified ...with Gaia in the previous papers in the series. By combining the periods from our catalog attributable to rotation with previously derived rotation periods for benchmark open clusters, we develop an empirical gyrochronology relation of angular momentum evolution that is valid for stars with ages 10–1000 Myr. Excluding stars rotating faster than 2 days, which we find are predominantly binaries, we achieve a typical age precision of ≈0.2–0.3 dex and improving at older ages. Importantly, these empirical relations apply to not only FGK-type stars but also M-type stars, due to the angular momentum distribution being much smoother, simpler, continuous, and monotonic as compared to the rotation period distribution. As a result, we are also able to begin tracing in fine detail the nature of angular momentum loss in low-mass stars as functions of mass and age. We characterize the stellar variability amplitudes of the cool stars as functions of mass and age, which may correlate with the starspot covering fractions. We also identify pulsating variables among the hotter stars in the catalog, including
δ
Scuti,
γ
Dor, and slowly pulsating B-type variables. These data represent an important step forward in being able to estimate precise ages of FGK- and M-type stars in the field, starting as early as the pre-main-sequence phase of evolution.
Abstract
It is not yet fully understood how planet formation affects the properties of host stars, in or out of a cluster; however, abundance trends can help us understand this process. We present a ...detailed chemical abundance analysis of six stars in Praesepe, a planet-hosting open cluster. Pr0201 is known to host a close-in (period of 4.4 days) giant planet (mass of 0.54
M
J
), while the other five cluster members in our sample (Pr0133, Pr0081, Pr0208, Pr0051, and Pr0076) have no detected planets according to measurements of radial velocity. Using high-resolution echelle spectra with high signal-to-noise ratio obtained with Keck/HIRES and a novel approach to measurements of equivalent width (XSpect-EW), we derived abundances of up to 20 elements spanning a range of condensation temperatures (
T
C
). We find a mean cluster metallicity of Fe/H = +0.21 ± 0.02 dex, in agreement with most previous determinations. We find most of our elements show an X/Fe scatter of ∼0.02–0.03 dex and conclude that our stellar sample is chemically homogeneous. The
T
C
slope for the cluster mean abundances is consistent with zero and none of the stars in our sample exhibit individually a statistically significant
T
C
slope. Using a planet engulfment model, we find that the planet host, Pr0201, shows no evidence of significant enrichment in its refractory elements when compared to the cluster mean that would be consistent with a planetary accretion scenario.
We develop an empirical model to estimate mass-loss rates via coronal mass ejections (CMEs) for solar-type pre-main-sequence (PMS) stars. Our method estimates the CME mass-loss rate from the observed ...energies of PMS X-ray flares, using our empirically determined relationship between solar X-ray flare energy and CME mass: log(M sub(CME)g) - 0.63 x log(E sub(flare)erg) - 2.57. Using masses determined for the largest flaring magnetic structures observed on PMS stars, we suggest that this solar-calibrated relationship may hold over 10 orders of magnitude in flare energy and 7 orders of magnitude in CME mass. The total CME mass-loss rate we calculate for typical solar-type PMS stars is in the range 10 super(-12)-10 super(-9) M sub(middot in circle) yr super(-1). We then use these CME mass-loss rate estimates to infer the attendant angular momentum loss leading up to the main sequence. Assuming that the CME outflow rate for a typical ~1 M sub(middot in circle) T Tauri star is <10 super(-10) M sub(middot in circle) yr super(-1), the resulting spin-down torque is too small during the first ~1 Myr to counteract the stellar spin-up due to contraction and accretion. However, if the CME mass-loss rate is gap 10 super(-10) M sub(middot in circle) yr super(-1), as permitted by our calculations, then the CME spin-down torque may influence the stellar spin evolution after an age of a few Myr.
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