- ID:
- ivo://CDS.VizieR/J/AJ/158/243
- Title:
- A search for multiplanet systems with TESS
- Short Name:
- J/AJ/158/243
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Transiting exoplanets in multiplanet systems exhibit non-Keplerian orbits as a result of the gravitational influence from companions, which can cause the times and durations of transits to vary. The amplitude and periodicity of the transit time variations are characteristic of the perturbing planet's mass and orbit. The objects of interest from the Transiting Exoplanet Survey Satellite (TESS) are analyzed in a uniform way to search for transit timing variations (TTVs) with sectors 1-3 of data. Due to the volume of targets in the TESS candidate list, artificial intelligence is used to expedite the search for planets by vetting nontransit signals prior to characterizing the light-curve time series. The residuals of fitting a linear orbit ephemeris are used to search for TTVs. The significance of a perturbing planet is assessed by comparing the Bayesian evidence between a linear and nonlinear ephemeris, which is based on an N-body simulation. Nested sampling is used to derive posterior distributions for the N-body ephemeris and in order to expedite convergence, custom priors are designed using machine learning. A dual-input, multi-output convolutional neural network is designed to predict the parameters of a perturbing body given the known parameters and measured perturbation (O-C). There is evidence for three new multiplanet candidates (WASP-18, WASP-126, TOI 193) with nontransiting companions using the two-minute cadence observations from TESS. This approach can be used to identify stars in need of longer radial velocity and photometric follow-up than those already performed.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/415/2417
- Title:
- ASK spectroscopic sequence of galaxies
- Short Name:
- J/MNRAS/415/2417
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify a spectroscopic sequence of galaxies, analogous to the Hubble sequence of morphological types, based on the Automatic Spectroscopic K-means-based (ASK) classification. Considering galaxy spectra as multidimensional vectors, the majority of the spectral classes are distributed along a well-defined curve going from the earliest to the latest types, suggesting that the optical spectra of normal galaxies can be described in terms of a single affine parameter. Optically bright active galaxies, however, appear as an independent, roughly orthogonal branch that intersects the main sequence exactly at the transition between early and late types.
- ID:
- ivo://CDS.VizieR/J/A+AS/125/229
- Title:
- A standard stellar library
- Short Name:
- J/A+AS/125/229
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The present library provides an extensive and homogeneous grid of low-resolution theoretical flux distributions for a large range of stellar parameters : Teff=50,000K to K, logg=5.50 to -1.02 and [M/H]=-5.0 to +1.0. The library has been constructed from different grids of blanketed stellar atmosphere models (Bessell et al. (1989A&AS...77....1B, 1991A&AS...89..335B), Fluks et al. (1994, Cat. <J/A+AS/105/311>), Kurucz (1995, priv. comm.), Allard & Hauschildt (1995ApJ...445..433A). The models described in the accompanying paper (Lejeune et al. (1997A&AS..125..229L) are given here as part of a more extensive data set including M dwarf model spectra, which will be presented in a forthcoming paper (Lejeune et al., 1998, Cat. <J/A+AS/130/65>). A correction procedure has been applied to the theoretical energy in order to calibrate fluxes on empirical-temperature relations (see also Lejeune et al., 1998, Cat. <J/A+AS/130/65>). The library is given here in its two versions : the first one (files *.ori) containing the "original" flux distributions -- as given by the original grids of atmosphere models --, but rebinned on a common wavelength scale (see also Leitherer et al. 1996PASP..108..996L) and the second one (files *.cor) which provides the "corrected" flux distributions. Each version of the library contains an ASCII file of models for each of the 19 values of the metallicity ([M/H]=-5.0, -4.5, -4.0, -3.5, -3.0, -2.5, -2.0, -1.5, -1.0, -0.5, -0.3, -0.2, -0.1, 0.0, +0.1, +0.2, +0.3, +0.5 and +1.0), named as lcbxxx.yyy, where xxx designates the metallicity (ex: 'm15' --> [M/H]=-1.5), and yyy identifies the library version. For each model (out of the total of 8315 models), a flux spectrum is given for the (same) set of 1221 wavelength points covering the range 9.1 to 160000 nm, with a mean resolution of 10{AA} in the UV and 20{AA} in the visible. In addition to the 19 metallicity files, two individual files originating from the Kurucz (1991, in Precision Photometry: Astrophysics of the Galaxy, Davis Philip A.G., Upgren A.R. & Janes K.A. (eds.). Schenectady, NY, L. Davis Press, Inc., 1991, pp. 27-44)) models are given, lcbsun.ori and lcbvega.ori, which provide theoretical flux distributions for the Sun and Vega respectively.
- ID:
- ivo://CDS.VizieR/J/A+AS/130/65
- Title:
- A standard stellar library. II.
- Short Name:
- J/A+AS/130/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A standard library of theoretical stellar spectra intended for multiple synthetic photometry applications including spectral evolutionary synthesis is presented. The grid includes M dwarf model spectra, hence complementing the first library version established in Paper I (Lejeune et al., 1997, Cat. <J/A+AS/125/229>). It covers the following wide ranges of fundamental parameters: Teff: 50,000 to 2000K, logg: 5.5 to -1.02, and [Fe/H]: +1.0 to -5.0. A correction procedure is also applied to the theoretical spectra in order to provide color-calibrated flux distributions over a large domain of effective temperatures. Empirical Teff-color calibrations are constructed between 11500K and 2000K, and semi-empirical calibrations for non-solar abundances ([Fe/H]=-3.5 to +1.0) are established. Model colors and bolometric corrections for both the original and the corrected spectra, synthesized in the UBV(RI)c(JHKLL'M) system, are given for the full range of stellar parameters. Synthetic colors: ---------------- Synthetic UBV(RI)c(JHKLM) colors have been computed from both the original and the corrected model flux distributions presented in Paper I (1997A&AS..125..229L; see catalog <J/A+AS/125/229>), as the files lcb98ori.dat and lcb98cor.dat respectively; the results are also presented in individual files lcb98xxx.ori and lcb98xxx.cor, where xxx designates the metallicity (ex: 'm15' --> [Fe/H]=-1.5). For each file, we give synthetic colors computed from energy-weighted and photon-weighted stellar fluxes. Semi-empirical calibrations: --------------------------- Empirical ([Fe/H]=0.0) and semi-empirical (-3.5<=[Fe/H]<=+1.0) Teff-colors (UBVRIJHKLM) calibrations are given in Tables 1 to 10.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/331
- Title:
- Astrometry in the Galactic Center
- Short Name:
- J/ApJ/725/331
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present significantly improved proper motion measurements of the Milky Way's central stellar cluster. These improvements are made possible by refining our astrometric reference frame with a new geometric optical distortion model for the W. M. Keck II 10m telescope's adaptive optics camera (NIRC2) in its narrow field mode. For the first time, this distortion model is constructed from on-sky measurements and is made available to the public in the form of FITS files. When applied to widely dithered images, it produces residuals in the separations of stars that are a factor of ~3 smaller compared with the outcome using previous models. By applying this new model, along with corrections for differential atmospheric refraction, to widely dithered images of SiO masers at the Galactic center (GC), we improve our ability to tie into the precisely measured radio Sgr A*-rest frame. The resulting infrared reference frame is ~2-3 times more accurate and stable than earlier published efforts. In this reference frame, Sgr A* is localized to within a position of 0.6mas and a velocity of 0.09mas/yr, or ~3.4km/s at 8kpc (1{sigma}). Also, proper motions for members of the central stellar cluster are more accurate, although less precise, due to the limited number of these wide field measurements. We define a reference frame with SiO masers and this reference frame's stability should improve steadily with future measurements of the SiO masers in this region ({propto}t^-3/2^). This is essential for achieving the necessary reference frame stability required to detect the effects of general relativity and extended mass on short-period stars at the GC.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/57
- Title:
- Atmosphere parameters model-derived for PMS & BDs
- Short Name:
- J/ApJ/805/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We test state-of-the-art model atmospheres for young very-low-mass stars and brown dwarfs in the infrared, by comparing the predicted synthetic photometry over 1.2-24{mu}m to the observed photometry of M-type spectral templates in star-forming regions. We find that (1) in both early and late young M types, the model atmospheres imply effective temperatures (Teff) several hundred Kelvin lower than predicted by the standard pre-main sequence (PMS) spectral type-Teff conversion scale (based on theoretical evolutionary models). It is only in the mid-M types that the two temperature estimates agree. (2) The Teff discrepancy in the early M types (corresponding to stellar masses >~0.4M_{sun}_ at ages of a few Myr) probably arises from remaining uncertainties in the treatment of atmospheric convection within the atmospheric models, whereas in the late M types it is likely due to an underestimation of dust opacity. (3) The empirical and model-atmosphere J-band bolometric corrections are both roughly flat, and similar to each other, over the M-type Teff range. Thus the model atmospheres yield reasonably accurate bolometric luminosities (Lbol), but lead to underestimations of mass and age relative to evolutionary expectations (especially in the late M types) due to lower Teff. We demonstrate this for a large sample of young Cha I and Taurus sources. (4) The trends in the atmospheric model J-K_s_ colors, and their deviations from the data, are similar at PMS and main sequence ages, suggesting that the model dust opacity errors we postulate here for young ages also apply at field ages.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/146
- Title:
- Atmospheric parameters for nearby B-F stars
- Short Name:
- J/ApJ/804/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Age determination is undertaken for nearby early type (BAF) stars, which constitute attractive targets for high-contrast debris disk and planet imaging surveys. Our analysis sequence consists of acquisition of ubvy{beta} photometry from catalogs, correction for the effects of extinction, interpolation of the photometry onto model atmosphere grids from which atmospheric parameters are determined, and finally, comparison to the theoretical isochrones from pre-main sequence through post-main sequence stellar evolution models, accounting for the effects of stellar rotation. We calibrate and validate our methods at the atmospheric parameter stage by comparing our results to fundamentally determined T_eff_ and log g values. We validate and test our methods at the evolutionary model stage by comparing our results on ages to the accepted ages of several benchmark open clusters (IC2602, {alpha} Persei, Pleiades, Hyades). Finally, we apply our methods to estimate stellar ages for 3493 field stars, including several with directly imaged exoplanet candidates.
- ID:
- ivo://CDS.VizieR/J/A+A/350/955
- Title:
- Atmospheric parameters in metal-poor stars. II
- Short Name:
- J/A+A/350/955
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present non-LTE corrections to abundances of Fe, O, Na, and Mg derived from LTE analyses of F-K stars over a broad range of gravities and metal abundances; they were obtained using statistical equilibrium calculations and new model atoms. Line opacity was considered by means of an empirical procedure where it was attributed to a veil of weak Fe I lines; in the case of solar-type dwarfs, results were compared with those obtained using (LTE) mean intensities computed from OSMARCS models. We think that the empirical procedure produces better results for metal-poor stars, while mean intensities should perhaps be preferred for the Sun (where departures from LTE are anyway not very large). Collisions with both electrons and H I atoms were considered. Since cross sections for this second mechanism are very poorly known, we calibrated them empirically by matching observations of RR Lyrae variables at minimum light (discussed in Clementini et al., 1995, Cat. <J/AJ/110/2319>). These stars were selected because non-LTE effects are expected to be larger in these stars than in those usually considered in the study of the chemical evolution of the Galaxy (cool main sequence and red giant branch stars). We found that different non-LTE mechanisms are important for the different species and transitions considered; on the whole, our calculations yielded moderate corrections to LTE abundances for high excitation O lines in warm dwarfs and giants, Na and Mg lines in giants and supergiants, and Fe I lines in F-supergiants (where corrections becomes very large for IR O lines). Non-LTE corrections were found to be negligible in the other cases studied.
- ID:
- ivo://CDS.VizieR/J/ApJ/844/139
- Title:
- Atomic mass excesses
- Short Name:
- J/ApJ/844/139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray burst model predictions of light curves and the final composition of the nuclear ashes are affected by uncertain nuclear masses. However, not all of these masses are determined experimentally with sufficient accuracy. Here we identify the remaining nuclear mass uncertainties in X-ray burst models using a one-zone model that takes into account the changes in temperature and density evolution caused by changes in the nuclear physics. Two types of bursts are investigated-a typical mixed H/He burst with a limited rapid proton capture process (rp-process) and an extreme mixed H/He burst with an extended rp-process. When allowing for a 3{sigma} variation, only three remaining nuclear mass uncertainties affect the light-curve predictions of a typical H/He burst (^27^P, ^61^Ga, and ^65^As), and only three additional masses affect the composition strongly (^80^Zr, ^81^Zr, and ^82^Nb). A larger number of mass uncertainties remain to be addressed for the extreme H/He burst, with the most important being ^58^Zn, ^61^Ga, ^62^Ge, ^65^As, ^66^Se, ^78^Y, ^79^Y, ^79^Zr, ^80^Zr, ^81^Zr, ^82^Zr, ^82^Nb, ^83^Nb, ^86^Tc, ^91^Rh, ^95^Ag, ^98^Cd, ^99^In, ^100^In, and ^101^In. The smallest mass uncertainty that still impacts composition significantly when varied by 3{sigma} is ^85^Mo with 16keV uncertainty. For one of the identified masses, ^27^P, we use the isobaric mass multiplet equation to improve the mass uncertainty, obtaining an atomic mass excess of -716(7)keV. The results provide a roadmap for future experiments at advanced rare isotope beam facilities, where all the identified nuclides are expected to be within reach for precision mass measurements.
- ID:
- ivo://CDS.VizieR/J/MNRAS/414/2602
- Title:
- Automated classification of HIP variables
- Short Name:
- J/MNRAS/414/2602
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an evaluation of the performance of an automated classification of the Hipparcos periodic variable stars into 26 types. The sub-sample with the most reliable variability types available in the literature is used to train supervised algorithms to characterize the type dependencies on a number of attributes. The most useful attributes evaluated with the random forest methodology include, in decreasing order of importance, the period, the amplitude, the V-I colour index, the absolute magnitude, the residual around the folded light-curve model, the magnitude distribution skewness and the amplitude of the second harmonic of the Fourier series model relative to that of the fundamental frequency.
