44 research outputs found
Red supergiant stars in the Large Magellanic Cloud. II. Infrared properties and mid-infrared variability
The characteristics of IR properties and MIR variability of RSGs in the LMC
are analyzed based on 12 bands of NIR to MIR co-added data from 2MASS, Spitzer
and WISE, and 6.6 years of MIR time-series data collected by the ALLWISE
and NEOWISE-R projects. 773 RSGs candidates were compiled from the literature
and verified by using the CMD, SED and MIR variability. About 15\% of valid
targets in the / diagram may show PAH emission. We
show that arbitrary dereddening Q parameters related to the IRAC4, S9W, WISE3,
WISE4, and MIPS24 bands could be constructed based on a precise measurement of
MIR interstellar extinction law. Several peculiar outliers in our sample are
discussed, in which one outlier might be a RSG right before the explosion or an
x-AGB star in the very late evolutionary stage based on the MIR spectrum and
photometry. There are 744 identified RSGs in the final sample having both the
WISE1- and WISE2-band time-series data. The results show that the MIR
variability is increasing along with the increasing of brightness. There is a
relatively tight correlation between the MIR variability, MLR, and the warm
dust or continuum, where the MIR variability is evident for the targets with
and , while the rest of the targets show
much smaller MIR variability. The MIR variability is also correlated with the
MLR for which targets with larger variability also show larger MLR with an
approximate upper limit of . Both the variability and the
luminosity may be important for the MLR since the WISE4-band flux is increasing
exponentially along with the degeneracy of luminosity and variability. The
identified RSG sample has been compared with the theoretical evolutionary
models and shown that the discrepancy between observation and evolutionary
models can be mitigated by considering both variability and extinction.Comment: 24 pages, 22 figures, A&A accepte
Gaia Data Release 3: The first Gaia catalogue of variable AGN
One of the novelties of the Gaia-DR3 with respect to the previous data
releases is the publication of the multiband light curves of about 1 million
AGN. The goal of this work was the creation of a catalogue of variable AGN,
whose selection was based on Gaia data only. We first present the
implementation of the methods to estimate the variability parameters into a
specific object study module for AGN. Then we describe the selection procedure
that led to the definition of the high-purity variable AGN sample and analyse
the properties of the selected sources. We started from a sample of millions of
sources, which were identified as AGN candidates by 11 different classifiers
based on variability processing. Because the focus was on the variability
properties, we first defined some pre-requisites in terms of number of data
points and mandatory variability parameters. Then a series of filters was
applied using only Gaia data and the Gaia Celestial Reference Frame 3
(Gaia-CRF3) sample as a reference.The resulting Gaia AGN variable sample, named
GLEAN, contains about 872000 objects, more than 21000 of which are new
identifications. We checked the presence of contaminants by cross-matching the
selected sources with a variety of galaxies and stellar catalogues. The
completeness of GLEAN with respect to the variable AGN in the last Sloan
Digital Sky Survey quasar catalogue is about 47%, while that based on the
variable AGN of the Gaia-CRF3 sample is around 51%. From both a comparison with
other AGN catalogues and an investigation of possible contaminants, we conclude
that purity can be expected to be above 95%. Multiwavelength properties of
these sources are investigated. In particular, we estimate that about 4% of
them are radio-loud. We finally explore the possibility to evaluate the time
lags between the flux variations of the multiple images of strongly lensed
quasars, and show one case.Comment: 19 pages, 31 figures, 2 table. This paper is part of Gaia Data
Release 3 (DR3). In press for A&
Evolved Massive Stars at Low-metallicity V. Mass-Loss Rate of Red Supergiant Stars in the Small Magellanic Cloud
We assemble the most complete and clean red supergiant (RSG) sample (2,121
targets) so far in the Small Magellanic Cloud (SMC) with 53 different bands of
data to study the MLR of RSGs. In order to match the observed spectral energy
distributions (SEDs), a theoretical grid of 17,820 Oxygen-rich models
(``normal'' and ``dusty'' grids are half-and-half) is created by the
radiatively-driven wind model of the DUSTY code, covering a wide range of dust
parameters. We select the best model for each target by calculating the minimal
modified chi-square and visual inspection. The resulting MLRs from DUSTY are
converted to real MLRs based on the scaling relation, for which a total MLR of
yr is measured (corresponding to a
dust-production rate of yr), with a
typical MLR of yr for the general population of
the RSGs. The complexity of mass-loss estimation based on the SED is fully
discussed for the first time, indicating large uncertainties based on the
photometric data (potentially up to one order of magnitude or more). The
Hertzsprung-Russell and luminosity versus median absolute deviation diagrams of
the sample indicate the positive relation between luminosity and MLR.
Meanwhile, the luminosity versus MLR diagrams show a ``knee-like'' shape with
enhanced mass-loss occurring above , which may
be due to the degeneracy of luminosity, pulsation, low surface gravity,
convection, and other factors. We derive our MLR relation by using a
third-order polynomial to fit the sample and compare our result with previous
empirical MLR prescriptions. Given that our MLR prescription is based on a much
larger sample than previous determinations, it provides a more accurate
relation at the cool and luminous region of the H-R diagram at low-metallicity
compared to previous studies.Comment: 16 pages, 19 figures, accepted by A&
DU439Module 14.1 Software Release Note: Gaia Report to ESA (GAIA-C4-SP-OPM-PG-013)
International audienc