- ID:
- ivo://CDS.VizieR/J/A+A/551/A113
- Title:
- Spectrum of VY CMa in 220.65-224.25GHz range
- Short Name:
- J/A+A/551/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first detection of pure rotational transitions of TiO and TiO2 at (sub-)millimeter wavelengths towards the red supergiant VYCMa. A rotational temperature, Trot, of about 250K was derived for TiO2. Although Trot was not well constrained for TiO, it is likely somewhat higher than that of TiO2. The detection of the Ti oxides confirms that they are formed in the circumstellar envelopes of cool oxygen-rich stars and may be the "seeds" of inorganic-dust formation, but alternative explanations for our observation of TiO and TiO2 in the cooler regions of the envelope cannot be ruled out at this time. The observations suggest that a significant fraction of the oxides is not converted to dust, but instead remains in the gas phase throughout the outflow.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/710/1142
- Title:
- SpeX spectroscopy of low mass binaries. I.
- Short Name:
- J/ApJ/710/1142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the identification of 17 candidate brown dwarf binaries whose components straddle the L dwarf/T dwarf transition. These sources were culled from a large near-infrared spectral sample of L and T dwarfs observed with the Infrared Telescope Facility SpeX spectrograph. Candidates were selected on the basis of spectral ratios which segregate known (resolved) L dwarf/T dwarf pairs from presumably single sources. Composite templates, constructed by combining 13581 pairs of absolute flux-calibrated spectra, are shown to provide statistically superior fits to the spectra of our 17 candidates as compared to single templates. Ten of these candidates appear to have secondary components that are significantly brighter than their primaries over the 1.0-1.3um band, indicative of rapid condensate depletion at the L dwarf/T dwarf transition. Our results support prior indications of enhanced multiplicity amongst early-type T dwarfs; 53+/-7% of the T0-T4 dwarfs in our spectral sample are found to be either resolved or unresolved (candidate) pairs, although this is consistent with an intrinsic (volume complete) brown dwarf binary fraction of only 15%. If verified, this sample of spectral binaries more than doubles the number of known L dwarf/T dwarf transition pairs, enabling a broader exploration of this poorly understood phase of brown dwarf atmospheric evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/832/58
- Title:
- Spitzer/IRAC monitoring of WISE J085510.83-071442.5
- Short Name:
- J/ApJ/832/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Because WISE J085510.83-071442.5 (hereafter WISE 0855-0714) is the coldest known brown dwarf (~250K) and one of the Sun's closest neighbors (2.2pc), it offers a unique opportunity to study a planet-like atmosphere in an unexplored regime of temperature. To detect and characterize inhomogeneities in its atmosphere (e.g., patchy clouds, hot spots), we have performed time-series photometric monitoring of WISE 0855-0714 at 3.6 and 4.5{mu}m with the Spitzer Space Telescope during two 23hr periods that were separated by several months. For both bands, we have detected variability with peak-to-peak amplitudes of 4%-5% and 3%-4% in the first and second epochs, respectively. The light curves are semiperiodic in the first epoch for both bands, but they are more irregular in the second epoch. Models of patchy clouds have predicted a large increase in mid-infrared (mid-IR) variability amplitudes (for a given cloud covering fraction) with the appearance of water ice clouds at T_eff_<375K, so if such clouds are responsible for the variability of WISE 0855-0714, then its small amplitudes of variability indicate a very small deviation in cloud coverage between hemispheres. Alternatively, the similarity in mid-IR variability amplitudes between WISE 0855-0714 and somewhat warmer T and Y dwarfs may suggest that they share a common origin for their variability (i.e., not water clouds). In addition to our variability data, we have examined other constraints on the presence of water ice clouds in the atmosphere of WISE 0855-0714, including the recent mid-IR spectrum from Skemer+ (2016ApJ...826L..17S). We find that robust evidence of such clouds is not yet available.
- ID:
- ivo://CDS.VizieR/J/ApJ/651/502
- Title:
- Spitzer IRAC photometry of M, L, and T dwarfs
- Short Name:
- J/ApJ/651/502
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a program to acquire photometry for 86 late M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data.
- ID:
- ivo://CDS.VizieR/J/ApJ/679/720
- Title:
- Spitzer observations of the Hyades
- Short Name:
- J/ApJ/679/720
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Spitzer Space Telescope to search for infrared excess at 24, 70, and 160um due to debris disks around a sample of 45 FGK-type members of the Hyades. We supplement our observations with archival 24 and 70um Spitzer data of an additional 22 FGK-type and 11 A-type Hyades members in order to provide robust statistics on the incidence of debris disks at 625Myr of age, an era corresponding to the late heavy bombardment in the solar system. We find that none of the 67 FGK-type stars in our sample show evidence for a debris disk, while 2 out of the 11 A-type stars do. This difference in debris disk detection rate is likely to be due to a sensitivity bias in favor of early-type stars. The fractional disk luminosity, L_dust_/L_*_, of the disks around the two A-type stars is ~4x10^-5^, a level that is below the sensitivity of our observations toward the FGK-type stars. However, our sensitivity limits for FGK-type stars are able to exclude, at the 2{sigma} level, frequencies higher than 12% and 5% of disks with L_dust_/L_*_>1x10^-4^ and L_dust_/L_*_>5x10^-4^, respectively. We also use our sensitivity limits and debris disk models to constrain the maximum mass of dust, as a function of distance from the stars, that could remain undetected around our targets.
- ID:
- ivo://CDS.VizieR/J/A+A/517/A44
- Title:
- Spitzer sources in the Galactic bulge
- Short Name:
- J/A+A/517/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a photometric catalogue of seven selected fields towards the Galactic bulge, observed with the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope with unprecedented sensitivity. The locations of the fields are defined in Figure 1 and Table 1 of the paper. In each of the fields, tens of thousands of point sources were detected. The catalogue is split up into seven tables, according to the different fields. Table 5 in the paper gives ten lines of the band-merged catalogue of the Bulge N1 field as an example. In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue. Besides a catalogue for each field, fits files of the IRAC and MIPS mosaics are presented, too. As a cautionary note for the users, we would like to add that the least reliable sources in our catalogue are those with detection in only one IRAC band and no MIPS detection, and with (i) either no 2MASS and DENIS counterpart (depending on the field, between 3.1% and 6.7% of the sources), or (ii) a DENIS and 2MASS counterpart at a distance between 1.6 and 3 arcseconds (depending on the field, between 0.4% and 1.0% of the sources).
- ID:
- ivo://CDS.VizieR/J/A+A/557/A26
- Title:
- STAGGER-grid of 3D stellar models. I.
- Short Name:
- J/A+A/557/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the STAGGER-grid, a comprehensive grid of time-dependent, three-dimensional (3D), hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~220 grid models range in effective temperature, Teff, from 4000 to 7000K in steps of 500K, in surface gravity, logg, from 1.5 to 5.0 in steps of 0.5dex, and metallicity, [Fe/H], from -4.0 to +0.5 in steps of 0.5 and 1.0dex.
- ID:
- ivo://CDS.VizieR/J/A+A/560/A8
- Title:
- STAGGER-grid of 3D stellar models. II.
- Short Name:
- J/A+A/560/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the implications of averaging methods with different reference depth scales for 3D hydrodynamical model atmospheres computed with the Stagger-code. The temporally and spatially averaged (hereafter denoted as <3D>) models are explored in the light of local thermodynamic equilibrium (LTE) spectral line formation by comparing spectrum calculations using full 3D atmosphere structures with those from <3D> averages. We explored methods for computing mean <3D> stratifications from the Stagger-grid time-dependent 3D radiative hydrodynamical atmosphere models by considering four different reference depth scales (geometrical depth, column-mass density, and two optical depth scales). Furthermore, we investigated the influence of alternative averages (logarithmic, enforced hydrostatic equilibrium, flux-weighted temperatures). For the line formation we computed curves of growth for FeI and FeII lines in LTE.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A89
- Title:
- STAGGER-grid of 3D stellar models. III.
- Short Name:
- J/A+A/573/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. The adiabatic entropy value of the deep convection zone, s_bot_, and the entropy jump, {Delta}s, determined from the 3D RHD models, are matched with the mixing length parameter, {alpha}_MLT_, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derive the mass mixing length, {alpha}_m_, and the vertical correlation length of the vertical velocity, C[V_z_,V_z_], directly from the 3D hydrodynamical simulations of stellar subsurface convection.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A90
- Title:
- STAGGER-grid of 3D stellar models. IV.
- Short Name:
- J/A+A/573/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compute the emergent stellar spectra from the UV to far infrared for different viewing angles using realistic 3D model atmospheres for a large range in stellar parameters to predict the stellar limb darkening. We have computed full 3D LTE synthetic spectra based on 3D radiative hydrodynamic atmosphere models from the Stagger-grid in the ranges: Teff from 4000 to 7000K, logg from 1.5 to 5.0, and [Fe/H], from -4.0 to +0.5. From the resulting intensities at different wavelength, we derived coefficients for the standard limb darkening laws considering a number of often-used photometric filters. Furthermore, we calculated theoretical transit light curves, in order to quantify the differences between predictions by the widely used 1D model atmosphere and our 3D models.
