scholarly journals Gaia Data Release 2

2018 ◽  
Vol 618 ◽  
pp. A58 ◽  
Author(s):  
N. Mowlavi ◽  
I. Lecoeur-Taïbi ◽  
T. Lebzelter ◽  
L. Rimoldini ◽  
D. Lorenz ◽  
...  
Keyword(s):  
Gravitational Lensing ◽  
Early Stage ◽  
Percent Level ◽  
Variable Stars ◽  
Light Curves ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Data Release ◽  
Regular Variable ◽  
Period Variable

Context. Gaia Data Release 2 (DR2) provides a unique all-sky catalogue of 550 737 variable stars, of which 151 761 are long-period variable (LPV) candidates with G variability amplitudes larger than 0.2 mag (5–95% quantile range). About one-fifth of the LPV candidates are Mira candidates, the majority of the rest are semi-regular variable candidates. For each source, G, GBP, and GRP photometric time-series are published, together with some LPV-specific attributes for the subset of 89 617 candidates with periods in G longer than 60 days. Aims. We describe this first Gaia catalogue of LPV candidates, give an overview of its content, and present various validation checks. Methods. Various samples of LPVs were used to validate the catalogue: a sample of well-studied very bright LPVs with light curves from the American Association of Variable Star Observers that are partly contemporaneous with Gaia light curves, a sample of Gaia LPV candidates with good parallaxes, the All-Sky Automated Survey for Supernovae catalogue of LPVs, and the Optical Gravitational Lensing Experiment (OGLE) catalogues of LPVs towards the Magellanic Clouds and the Galactic bulge. Results. The analyses of these samples show a good agreement between Gaia DR2 and literature periods. The same is globally true for bolometric corrections of M-type stars. The main contaminant of our DR2 catalogue comes from young stellar objects (YSOs) in the solar vicinity (within ~1 kpc), although their number in the whole catalogue is only at the percent level. A cautionary note is provided about parallax-dependent LPV attributes published in the catalogue. Conclusions. This first Gaia catalogue of LPVs approximately doubles the number of known LPVs with amplitudes larger than 0.2 mag, despite the conservative candidate selection criteria that prioritise low contamination over high completeness, and despite the limited DR2 time coverage compared to the long periods characteristic of LPVs. It also contains a small set of YSO candidates, which offers the serendipitous opportunity to study these objects at an early stage of the Gaia data releases.

scholarly journals The ASAS-SN catalogue of variable stars – VIII. ‘Dipper’ stars in the Lupus star-forming region

2020 ◽  
Vol 496 (3) ◽  
pp. 3257-3269 ◽  
Author(s):  
J W Bredall ◽  
B J Shappee ◽  
E Gaidos ◽  
T Jayasinghe ◽  
P Vallely ◽  
...  
Keyword(s):  
Main Sequence ◽  
Statistical Significance ◽  
Variable Stars ◽  
Young Stars ◽  
Light Curves ◽  
Young Stellar Objects ◽  
Circumstellar Dust ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri

ABSTRACT Some young stellar objects such as T Tauri-like ‘dipper’ stars vary due to transient partial occultation by circumstellar dust, and observations of this phenomenon inform us of conditions in the planet-forming zones close to these stars. Although many dipper stars have been identified with space missions such as Kepler/K2, ground-based telescopes offer longer term and multiwavelength perspectives. We identified 11 dipper stars in the Lupus star-forming region in data from the All-Sky Automated Survey for SuperNovae (ASAS-SN), and further characterized these using observations by the Las Cumbres Global Observatory Telescope (LCOGT) and the Transiting Exoplanet Survey Satellite (TESS), as well as archival data from other missions. Dipper stars were identified from a catalogue of nearby young stars and selected based on the statistical significance, asymmetry, and quasi-periodicity or aperiodicity of variability in their ASAS-SN light curves. All 11 stars lie above or redwards of the zero-age main sequence and have infrared (IR) excesses indicating the presence of full circumstellar discs. We obtain reddening–extinction relations for the variability of seven stars using our combined ASAS-SN-TESS and LCOGT photometry. In all cases, the slopes are below the ISM value, suggesting larger grains, and we find a tentative relation between the slope (grain size) and the $K_\text{s}-[22 \, \mu \text{m}]$ IR colour regarded as a proxy for disc evolutionary state.

scholarly journals An autoregressive model for irregular time series of variable stars

2016 ◽  
Vol 12 (S325) ◽  
pp. 259-262
Author(s):  
Susana Eyheramendy ◽  
Felipe Elorrieta ◽  
Wilfredo Palma
Keyword(s):  
Time Series ◽  
Gravitational Lensing ◽  
Autoregressive Model ◽  
Likelihood Estimation ◽  
Estimation Procedure ◽  
Variable Stars ◽  
Light Curves ◽  
Finite Sample ◽  
Harmonic Model ◽  
Dependency Structure

AbstractThis paper discusses an autoregressive model for the analysis of irregularly observed time series. The properties of this model are studied and a maximum likelihood estimation procedure is proposed. The finite sample performance of this estimator is assessed by Monte Carlo simulations, showing accurate estimators. We implement this model to the residuals after fitting an harmonic model to light-curves from periodic variable stars from the Optical Gravitational Lensing Experiment (OGLE) and Hipparcos surveys, showing that the model can identify time dependency structure that remains in the residuals when, for example, the period of the light-curves was not properly estimated.

scholarly journals Bipolar Outflows and Stellar Jets

1987 ◽  
Vol 115 ◽  
pp. 213-237 ◽  
Author(s):  
Ronald L. Snell
Keyword(s):  
Physical Properties ◽  
High Velocity ◽  
Molecular Clouds ◽  
Early Stage ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Bipolar Outflows ◽  
Stellar Objects ◽  
Stellar Jets ◽  
Almost All

A wealth of data is now available on the energetic mass outflows that are associated with young stellar objects. This phenomenon is thought to occur at a very early stage in the evolution of stars of almost all masses. The discovery of this energetic event was first made through observations of the rapidly expanding molecular gas that surrounds many of these young stellar objects. A review of the physical properties, including the energetics and morphology, of the expanding molecular gas is presented in this paper. In addition, the role these energetic winds play in affecting the dynamics of the parental molecular clouds is also discussed. Finally, the results of detailed studies of the structure and kinematics of the high velocity molecular gas are reviewed and the evidence for existance of wind-swept cavities and molecular shells within the clouds are presented.

scholarly journals Ongoing astrometric microlensing events of two nearby stars

2018 ◽  
Vol 615 ◽  
pp. L11 ◽  
Author(s):  
J. Klüter ◽  
U. Bastian ◽  
M. Demleitner ◽  
J. Wambsganss
Keyword(s):  
Prior Knowledge ◽  
Gravitational Lensing ◽  
Proper Motion ◽  
Absolute Magnitude ◽  
Stellar Objects ◽  
Lens Position ◽  
Data Release ◽  
Nearby Stars ◽  
Excellent Tool ◽  
Background Star

Context. Astrometric microlensing is an excellent tool to determine the mass of stellar objects. By measuring the astrometric shift of a background source star in combination with precise predictions of its unlensed position and of the lens position, gravitational lensing allows to one determine the mass of the lensing star with a precision of 1%, independently of any prior knowledge. Aims. Making use of the recently published Gaia Data Release 2 (Gaia DR2) we predict astrometric microlensing events by fore-ground stars of high proper motion passing by a background star in the coming years. Methods. We compile a list of approximately 148 000 high-proper-motion stars within Gaia DR2 with µtot > 150 mas yr−1. We then search for background stars close to their paths and calculate the dates and separations of the closest approaches. Using color and absolute magnitude, we determine approximate masses of the lenses. Finally, we calculate the expected astrometric shifts and magnifications of the predicted events. Results. We detect two ongoing microlensing events by the high-proper-motion stars Luyten 143-23 and Ross 322 and predict closest separations of (108.5 ± 1.4) mas in July 2018 and (125.3 ± 3.4) mas in August 2018, respectively. The respective expected astrometric shifts are (1.74 ± 0.12) mas and (0.76 ± 0.06) mas. Furthermore, Luyten 143-23 will pass by another star in March 2021 with a closest separation of (280.1 ± 1.1) mas, which results in an expected shift of (0.69 ± 0.05) mas.

scholarly journals Early-stage young stellar objects in the Small Magellanic Cloud

2012 ◽  
Vol 428 (4) ◽  
pp. 3001-3033 ◽  
Author(s):  
J. M. Oliveira ◽  
J. Th. van Loon ◽  
G. C. Sloan ◽  
M. Sewiło ◽  
K. E. Kraemer ◽  
...  
Keyword(s):  
Early Stage ◽  
Magellanic Cloud ◽  
Young Stellar Objects ◽  
Small Magellanic Cloud ◽  
Stellar Objects

scholarly journals Comparison of Mean Light Curve Parameters of M, S and C Mira and Semi-Regular Variable Stars Using 75 Years of AAVSO Data

2000 ◽  
Vol 177 ◽  
pp. 165-170
Author(s):  
Marie-Odile Mennessier ◽  
Hichame Boughaleb ◽  
Janet A. Mattei
Keyword(s):  
Light Curve ◽  
Variable Stars ◽  
Light Curves ◽  
Long Period ◽  
Regular Variable

Using 75 years of AAVSO data, mean light curve parameters of a sample of 350 long-period M, S and C Mira and semi-regular variable stars have been investigated. We compare M, S and C Mira and semi-regular stars, present a classification of the light curves of LPVs and give discriminant parameters.

scholarly journals Modeling of Circumstellar Dust by the DUSTY Code

2011 ◽  
Vol 7 (S282) ◽  
pp. 247-250
Author(s):  
Tomislav Jurkić ◽  
Dubravka Kotnik-Karuza
Keyword(s):  
Near Infrared ◽  
Dynamical Behaviour ◽  
Light Curves ◽  
Young Stellar Objects ◽  
Numerical Code ◽  
Circumstellar Dust ◽  
Be Stars ◽  
Stellar Objects ◽  
Near Ir ◽  
Dust Temperature

AbstractWe present a circumstellar dust model around the symbiotic Mira RR Tel obtained by modeling the near-infrared JHKL magnitudes and ISO spectra. In order to follow the evolution of infrared colours in time, the published JHKL magnitudes were corrected by removing the Mira pulsations. The RR Tel light curves show three obscuration events in the near-IR. Using the simultaneously available JHKL magnitudes and ISO spectra in three different epochs, we obtained SEDs in the near- and mid-IR spectral region (1-20 μm) in epochs with and without obscuration.The DUSTY numerical code was used to solve the radiative transfer and to determine the circumstellar dust properties of the inner dust regions around the Mira, assuming a spherical dust temperature distribution in its close neighbourhood. The physical properties of the dust, mass loss and optical depth during intervals with and without obscuration have been obtained. Both JHKL and ISO observations during the obscuration period can be reproduced with a spherical dust envelope, while ISO spectra outside obscuration show a different behaviour. The dynamical behaviour of the circumstellar dust was obtained by modeling the JHKL magnitudes observed during the span of more than 30 years.The DUSTY code was also successfully applied in the modeling of circumstellar dust envelopes of young stellar objects, such as Herbig Ae/Be stars.

scholarly journals Theoretical Modes Fitting on Miras Light Curves

1993 ◽  
Vol 134 ◽  
pp. 139-140
Author(s):  
D. Barthés ◽  
Y. Tuchman ◽  
M. O. Mennessier ◽  
J. A. Mattei
Keyword(s):  
Power Spectrum ◽  
American Association ◽  
Variable Stars ◽  
Stellar Model ◽  
Light Curves ◽  
Long Period ◽  
Period Variable ◽  
The Common ◽  
Comparison Of The Results ◽  
Two Peaks

Visual observations of long period variable stars over 20 years were provided by the American Association of Variable Stars Observers, and were analysed as part of the preparation of the HIPPARCOS mission.A set of frequencies is extracted from the light curve by using Fourier transform, preliminary Van Cittert deconvolution and comparison of the results obtained through different kinds of spectral windows. The same procedure is applied to the residual obtained after nonlinear fit of the main frequency. After final comparison of both sets, a nonlinear fit of the common frequencies gives the ‘clean’ power spectrum.Different equilibrium stellar model (i) give theoretical linear nonadiabatic pulsation modes (vj) with their growth rates (ηj)i) (Tuchman 1978). The metallicity is taken between 0.005 and 0.02; the mixing length is λ = 1±0.2; the upper bound is r = 0.7. Assuming two peaks of the power spectrum to be the fundamental (vo) and first overtone (v1) modes, one looks for the corresponding models. The best one is selected by checking the other theoretical overtones they give. So are obtained the mass, the luminosity, the effective temperature and the effective radius of each star.

scholarly journals Physics and Evolution of LPVs from HIPPARCOS Kinematics

1999 ◽  
Vol 191 ◽  
pp. 117-122 ◽  
Author(s):  
M.O. Mennessier ◽  
R. Alvarez ◽  
X. Luri ◽  
M. Noirhomme-Fraiture ◽  
E. Rouard
Keyword(s):  
Variable Stars ◽  
Light Curves ◽  
Astronomical Data ◽  
Long Period ◽  
Period Variable

The HIPPARCOS satellite provides astronomical data for about one thousand Long Period Variable stars (LPVs) from which kinematics properties and luminosity calibrations in several bandpasses are deduced using an appropriate method. Several results are deduced: a classification of the LPVs and its relation with the classification from the light curves, a calibration of luminosities inducing properties (age, mass, etc.) along the AGB and a comparison of oxygen to carbon-rich stars.

scholarly journals Confirmation of monoperiodicity above 20 s for two blue large-amplitude pulsators

2020 ◽  
Vol 496 (2) ◽  
pp. 1105-1114 ◽  
Author(s):  
Paul Ross McWhirter ◽  
Marco C Lam ◽  
Iain A Steele
Keyword(s):  
Gravitational Lensing ◽  
Large Amplitude ◽  
Variable Stars ◽  
Light Curves ◽  
Driving Mechanism ◽  
New Class ◽  
Pulsating Variable Stars ◽  
Short Period ◽  
Filter Frequency ◽  
High Cadence

ABSTRACT Blue large-amplitude pulsators (BLAPs) are a new class of pulsating variable stars. They are located close to the hot subdwarf branch in the Hertzsprung–Russell diagram and have spectral classes of late O or early B. Stellar evolution models indicate that these stars are likely radially pulsating, driven by iron group opacity in their interiors. A number of variable stars with a similar driving mechanism exist near the hot subdwarf branch with multiperiodic oscillations caused by either pressure (p) or gravity (g) modes. No multiperiodic signals were detected in the OGLE (Optical Gravitational Lensing Experiment) discovery light curves since it would be difficult to detect short-period signals associated with higher order p modes with the OGLE cadence. Using the RISE instrument on the Liverpool Telescope, we produced high-cadence light curves of two BLAPs, OGLE-BLAP-009 (mv = 15.65 mag) and OGLE-BLAP-014 (mv = 16.79 mag), using a 720 nm longpass filter. Frequency analysis of these light curves identifies a primary oscillation with a period of 31.935 ± 0.0098 min and an amplitude from a Fourier series fit of 0.236 mag for BLAP-009. The analysis of BLAP-014 identifies a period of 33.625 ± 0.0214 min and an amplitude of 0.225 mag. Analysis of the residual light curves reveals no additional short-period variability down to an amplitude of 15.20 ± 0.26 mmag for BLAP-009 and 58.60 ± 3.44 mmag for BLAP-014 for minimum periods of 20 and 60 s, respectively. These results further confirm that the BLAPs are monoperiodic.

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