分类： 天文学 >> 天文学 提交时间： 2023-02-19
L. M. Sarro
A. Berihuete
R. L. Smart
C. Reylé
D. Barrado
M. García-Torres
W. J. Cooper
H. R. A. Jones
F. Marocco
O. L. Creevey
R. Sordo
C. A. L. Bailer-Jones
P. Montegriffo
R. Carballo
R. Andrae
M. Fouesneau
A. C. Lanzafame
F. Pailler
F. Thévenin
A. Lobel
摘要： Aims. In this work we use the Gaia DR3 set of ultracool dwarf candidates and complement the Gaia spectrophotometry with additional photometry in order to characterise its global properties. This includes the inference of the distances, their locus in the Gaia colour-absolute magnitude diagram and the (biased through selection) luminosity function in the faint end of the Main Sequence. We study the overall changes in the Gaia RP spectra as a function of spectral type. We study the UCDs in binary systems, attempt to identify low-mass members of nearby young associations, star forming regions and clusters, and analyse their variability properties. Results. We detect 57 young, kinematically homogeneous groups some of which are identified as well known star forming regions, associations and clusters of different ages. We find that the primary members of 880 binary systems with a UCD belong mainly to the thin and thick disk components of the Milky Way. We identify 1109 variable UCDs using the variability tables in the Gaia archive, 728 of which belong to the star forming regions defined by HMAC. We define two groups of variable UCDs with extreme bright or faint outliers. Conclusions. The set of sources identified as UCDs in the Gaia archive contains a wealth of information that will require focused follow-up studies and observations. It will help to advance our understanding of the nature of the faint end of the Main Sequence and the stellar/substellar transition.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Gaia Collaboration
S. A. Klioner
L. Lindegren
F. Mignard
J. Hernández
M. Ramos-Lerate
U. Bastian
M. Biermann
A. Bombrun
A. de Torres
E. Gerlach
R. Geyer
T. Hilger
D. Hobbs
U. L. Lammers
P. J. McMillan
H. Steidelmüller
D. Teyssier
C. M. Raiteri
S. Bartolomé
摘要： Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. We describe the construction of Gaia-CRF3, and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasars (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). The Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13 to 21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 ${\mu}$as yr${}^{-1}$ on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but exceeds 4 mas in either coordinate for 127 sources. We outline the future of the Gaia-CRF in the next Gaia data releases.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
H. Zhao
M. Schultheis
T. Zwitter
C. A. L. Bailer-Jones
P. Panuzzo
P. Sartoretti
G. M. Seabroke
A. Recio-Blanco
P. de Laverny
G. Kordopatis
O. L. Creevey
T. E. Dharmawardena
Y. Frémat
R. Sordo
R. Drimmel
D. J. Marshall
P. A. Palicio
G. Contursi
M. A. Álvarez
S. Baker
摘要： Studies of the correlation between different diffuse interstellar bands (DIBs) are important for exploring their origins. However, the Gaia-RVS spectral window between 846 and 870 nm contains few DIBs, the strong DIB at 862 nm being the only convincingly confirmed one. Here we attempt to confirm the existence of a broad DIB around 864.8 nm and estimate its characteristics using the stacked Gaia-RVS spectra of a large number of stars. We study the correlations between the two DIBs at 862 nm and 864.8 nm, as well as the interstellar extinction. We obtained spectra of the interstellar medium absorption by subtracting the stellar components using templates constructed from real spectra at high Galactic latitudes with low extinctions. We then stacked the ISM spectra in Galactic coordinates, pixelized by the HEALPix scheme, to measure the DIBs. The stacked spectrum is modeled by the profiles of the two DIBs, Gaussian for $\lambda$862 and Lorentzian for $\lambda$864.8, and a linear continuum. We obtain 8458 stacked spectra in total, of which 1103 (13%) have reliable fitting results after applying numerous conservative filters. This work is the first of its kind to fit and measure $\lambda$862 and $\lambda$864.8 simultaneously in cool-star spectra. We find that the EWs and CDs of the two DIBs are well correlated with each other. The full width at half maximum (FWHM) of $\lambda$864.8 is estimated as $1.62 \pm 0.33$ nm which compares to $0.55 \pm 0.06$ nm for $\lambda$862. We also measure the vacuum rest-frame wavelength of $\lambda$864.8 to be $\lambda_0 = 864.53 \pm 0.14$ nm, smaller than previous estimates. We find a solid confirmation of the existence of the DIB around 864.8 nm based on an exploration of its correlation with $\lambda$862 and estimation of its FWHM. $\lambda$862 correlates better with E(BP-RP) than $\lambda$864.8.
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