- ID:
- ivo://CDS.VizieR/J/A+A/573/A67
- Title:
- Fundamental stellar parameters from PolarBase
- Short Name:
- J/A+A/573/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The general context of this study is the inversion of stellar fundamental parameters from high-resolution Echelle spectra. We aim at developing a fast and reliable tool for the post-processing of spectra produced by ESPaDOnS and Narval spectropolarimeters. Our inversion tool relies on principal component analysis. It allows reducing dimensionality and defining a specific metric for the search of nearest neighbours between an observed spectrum and a set of observed spectra taken from the Elodie stellar library. Effective temperature, surface gravity, total metallicity, and projected rotational velocity are derived. Various tests presented in this study that were based solely on information coming from a spectral band centred on the Mgi b-triplet and had spectra from FGK stars are very promising.
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- ID:
- ivo://CDS.VizieR/J/ApJS/193/23
- Title:
- Fundamental stellar parameters in 47 Tucanae
- Short Name:
- J/ApJS/193/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fundamental parameters and time evolution of mass loss are investigated for post-main-sequence stars in the Galactic globular cluster 47 Tucanae (NGC 104). This is accomplished by fitting spectral energy distributions (SEDs) to existing optical and infrared photometry and spectroscopy, to produce a true Hertzsprung-Russell diagram. We confirm the cluster's distance as d=4611^+213^_-200_pc and age as 12+/-1Gyr. Horizontal branch models appear to confirm that no more red giant branch mass loss occurs in 47 Tuc than in the more metal-poor {omega} Centauri, though difficulties arise due to inconsistencies between the models. Using our SEDs, we identify those stars that exhibit infrared excess, finding excess only among the brightest giants: dusty mass loss begins at a luminosity of ~1000L_{sun}_, becoming ubiquitous above L=2000L_{sun}_. Recent claims of dust production around lower-luminosity giants cannot be reproduced, despite using the same archival Spitzer imagery.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A102
- Title:
- FU Ori multi-band interferometric observations
- Short Name:
- J/A+A/646/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- FU Orionis is the archetypal FUor star, a subclass of young stellar object (YSO) that undergo rapid brightening events, often gaining 4-6 magnitudes on timescales of days. This brightening is often associated with a massive increase in accretion; one of the most ubiquitous processes in astrophysics from planets and stars to super-massive black holes. We present multi-band interferometric observations of the FU Ori circumstellar environment, including the first J-band interferometric observations of a YSO. We investigate the morphology and temperature gradient of the inner-most regions of the accretion disk around FU Orionis. We aim to characterise the heating mechanisms of the disk and comment on potential outburst triggering processes. Methods. Recent upgrades to the MIRC-X instrument at the CHARA array allowed the first dual-band J and H observations of YSOs. Using baselines up to 331m, we present high angular resolution data of a YSO covering the near-infrared bands J, H, and K. The unprecedented spectral range of the data allows us to apply temperature gradient models to the innermost regions of FU Ori. We spatially resolve the innermost astronomical unit of the disk and determine the exponent of the temperature gradient of the inner disk to T{prop.to}r^-0.74+/-0.02^. This agrees with theoretical work that predicts T{prop.to}r^-0.75^ for actively accreting, steady state disks, a value only obtainable through viscous heating within the disk. We find a disk which extends down to the stellar surface at 0.015+/-0.007au where the temperature is found to be 5800+/-700K indicating boundary layer accretion. We find a disk inclined at 32+/-4{deg} with a minor-axis position angle of 34+/-11{deg}.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A79
- Title:
- FU Orionis small-amplitude light variations
- Short Name:
- J/A+A/618/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate small-amplitude light variations in FU Ori occurring in timescales of days and weeks. We seek to determine the mechanisms that lead to these light changes. Methods. The visual light curve of FU Ori gathered by the MOST satellite continuously for 55 days in the 2013-2014 winter season and simultaneously obtained ground-based multi-colour data were compared with the results from a disc and star light synthesis model. Hotspots on the star are not responsible for the majority of observed light variations. Instead, we found that the long periodic family of 10.5-11.4d (presumably) quasi-periods showing light variations up to 0.07 mag may arise owing to the rotational revolution of disc inhomogeneities located between 16-20 solar radii. The same distance is obtained by assuming that these light variations arise because of a purely Keplerian revolution of these inhomogeneities for a stellar mass of 0.7 solar mass. The short-periodic (3-1.38d) small amplitude (0.01mag) light variations show a clear sign of period shortening, similar to what was discovered in the first MOST observations of FU Ori. Our data indicate that these short-periodic oscillations may arise because of changing visibility of plasma tongues (not included in our model), revolving in the magnetospheric gap and/or likely related hotspots as well. Results obtained for the long-periodic 10-11d family of light variations appear to be roughly in line with the colour-period relation, which assumes that longer periods are produced by more external and cooler parts of the disc. Coordinated observations in a broad spectral range are still necessary to fully understand the nature of the short-periodic 1-3d family of light variations and their period changes.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A39
- Title:
- 7 FU Orionis-type stars CO spectral cubes
- Short Name:
- J/A+A/607/A39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- FU Orionis-type objects are pre-main sequence, low-mass stars with large outbursts in visible light that last for several years or decades. They are thought to represent an evolutionary phase during the life of every young star when accretion from the circumstellar disk is enhanced during recurring time periods. These outbursts are able to rapidly build up the star while affecting the physical conditions inside the circumstellar disk and thus the ongoing or future planet formation. In many models, infall from a circumstellar envelope seems to be necessary to trigger the outbursts. We characterise the morphology and the physical parameters of the circumstellar material around FU Orionis-type stars using the emission of millimetre-wavelength molecular tracers. The high-spatial-resolution study provides insight into the evolutionary state of the objects, the distribution of parameters in the envelopes and the physical processes forming the environment of these stars. We observed the J=1-0 rotational transition of ^13^CO and C^18^O towards eight northern FU Orionis-type stars (V1057 Cyg, V1515 Cyg, V2492 Cyg, V2493 Cyg, V1735 Cyg, V733 Cep, RNO 1B and RNO 1C) and determine the spatial and velocity structure of the circumstellar gas on a scale of a few thousand AU. We derive temperatures and envelope masses and discuss the kinematics of the circumstellar material.
- ID:
- ivo://CDS.VizieR/J/PASP/121/634
- Title:
- FUSE observations in Magellanic Clouds
- Short Name:
- J/PASP/121/634
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an atlas of stellar sight line data from the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite for 287 stars in the Magellanic Clouds, obtained from eight years of satellite operations. The intent of our project is to make this rich ensemble data set accessible to a broad community of researchers in a standardized format that will enable easy identification of subsets of these data that are appropriate for pursuing specific science programs. We present the data in a standardized manner, showing key interstellar lines on a velocity scale, optical (MCELS) and infrared (Spitzer) sight line context images, and overview plots of the spectral region containing the OVI {lambda}{lambda}1032, 1038 doublet, and the entire 905-1187{AA} spectral range observed with FUSE. Objects with multiple observations have had their data summed to directly provide the highest signal-to-noise ratio available. These data are accessible online as a High Level Science Product through the Multimission Archive at Space Telescope (MAST). In this article, we describe the data sets and processing, the atlas materials, and the MAST interface in detail, and also provide examples of how to use these materials.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/25
- Title:
- FUSE spectra analysis of hot subdwarf stars
- Short Name:
- J/ApJ/764/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- When the neutral interstellar medium is exposed to extreme-ultraviolet and soft X-ray radiation, the argon atoms in it are far more susceptible to being ionized than the hydrogen atoms. We make use of this fact to determine the level of ionization in the nearby warm neutral medium. By analyzing Far-Ultraviolet Spectroscopic Explorer observations of ultraviolet spectra of 44 hot subdwarf stars a few hundred parsecs away from the Sun, we can compare column densities of Ar I to those of O I, where the relative ionization of oxygen can be used as a proxy for that of hydrogen. The measured deficiency [ArI/OI]=-0.427+/-0.11dex below the expectation for a fully neutral medium implies that the electron density n(e){approx}0.04/cm3 if n(H)=0.5/cm3. This amount of ionization is considerably larger than what we expect from primary photoionizations resulting from cosmic rays, the diffuse X-ray background, and X-ray emitting sources within the medium, along with the additional ionizations caused by energetic secondary photoelectrons, Auger electrons, and photons from helium recombinations. We favor an explanation that bursts of radiation created by previous, nearby supernova remnants that have faded by now may have elevated the ionization, and the gas has not yet recombined to a quiescent level. A different alternative is that the low-energy portion of the soft X-ray background is poorly shielded by the H I because it is frothy and has internal pockets of very hot, X-ray emitting gases.
- ID:
- ivo://CDS.VizieR/J/ApJ/647/328
- Title:
- FUSE survey of OVI in ISM
- Short Name:
- J/ApJ/647/328
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of diffuse OVI emission in the interstellar medium (ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Spanning 5.5yr of FUSE observations, from launch through 2004 December, our data set consists of 2925 exposures along 183 sight lines, including all of those with previously published OVI detections. The data were processed using an implementation of CalFUSE version 3.1 modified to optimize the signal-to-noise ratio and velocity scale of spectra from an aperture-filling source.
- ID:
- ivo://CDS.VizieR/J/ApJS/176/59
- Title:
- FUSE survey of OVI in the disk of the Milky Way
- Short Name:
- J/ApJS/176/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To probe the distribution and physical characteristics of interstellar gas at temperatures T~3x10^5^K in the disk of the Milky Way, we have used the Far Ultraviolet Spectroscopic Explorer (FUSE) to observe absorption lines of OVI{lambda}1032 toward 148 early-type stars situated at distances >1kpc. After subtracting off a mild excess of OVI arising from the Local Bubble, combining our new results with earlier surveys of OVI, and eliminating stars that show conspicuous localized X-ray emission, we find an average OVI midplane density n_0_=1.3x10^-8^cm^-3^. The density decreases away from the plane of the Galaxy in a way that is consistent with an exponential scale height of 3.2kpc at negative latitudes or 4.6kpc at positive latitudes.
- ID:
- ivo://CDS.VizieR/J/ApJ/647/312
- Title:
- FUSE survey of OVI in the Milky Way
- Short Name:
- J/ApJ/647/312
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of OVI {lambda}1032 emission in the Milky Way using data from the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. The observations span the period from launch in 1999 to 2003 July. Our survey contains 112 sight lines, 23 of which show measurable OVI {lambda}1032 emission. The OVI {lambda}1032 emission feature was detected at all latitudes and exhibits intensities of 1900-8600photons/s/cm^2^/sr. Combined with values from the literature, these emission measurements are consistent with the picture derived from recent OVI absorption surveys: high-latitude sight lines probe OVI-emitting gas in a clumpy, thick disk or halo, while low-latitude sight lines sample mixing layers and interfaces in the thin disk of the Galaxy.