Gaia Early Data Release 3 Hodgkin, S. T.; Harrison, D. L.; Breedt, E. ...
Astronomy and astrophysics (Berlin),
08/2021, Letnik:
652
Journal Article
Recenzirano
Odprti dostop
Context.
Since July 2014, the
Gaia
mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky.
Aims.
We present the
...Gaia
Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by
Gaia
.
Methods.
We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to
Gaia
and (2)
Gaia
sources which have undergone a significant brightening or fading. Validation of the
Gaia
transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours.
Results.
We show that the
Gaia
Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae,
C
E
= 0.46, is dominated by the
Gaia
scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is
C
I
= 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec.
Conclusions.
The per-transit photometry for
Gaia
transients is precise to 1% at
G
= 13, and 3% at
G
= 19. The per-transit astrometry is accurate to 55 mas when compared to
Gaia
DR2. The
Gaia
Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge.
Abstract
The Astropy Project supports and fosters the development of open-source and openly developed
Python
packages that provide commonly needed functionality to the astronomical community. A key ...element of the Astropy Project is the core package
astropy
, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package, as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of interoperable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy Project.
We report on the discovery of HAT-P-12b, a transiting extrasolar planet orbiting the moderately bright V 12.8 K4 dwarf GSC 03033 - 00706, with a period P = 3.2130598 +/- 0.0000021 d, transit epoch Tc ...= 2454419.19556 +/- 0.00020 (BJD), and transit duration 0.0974 +/- 0.0006 d. The host star has a mass of 0.73 +/- 0.02 M, radius of 0.70+0.02 -0.01 R, effective temperature 4650 +/- 60 K, and metallicity Fe/H = -0.29 +/- 0.05. We find a slight correlation between the observed spectral line bisector spans and the radial velocity, so we consider, and rule out, various blend configurations including a blend with a background eclipsing binary, and hierarchical triple systems where the eclipsing body is a star or a planet. We conclude that a model consisting of a single star with a transiting planet best fits the observations, and show that a likely explanation for the apparent correlation is contamination from scattered moonlight. Based on this model, the planetary companion has a mass of 0.211 +/- 0.012 M J and radius of 0.959+0.029 -0.021 R J yielding a mean density of 0.295 +/- 0.025 g cm-3. Comparing these observations with recent theoretical models, we find that HAT-P-12b is consistent with a ~1-4.5 Gyr, mildly irradiated, H/He-dominated planet with a core mass MC 10 M {circled plus}. HAT-P-12b is thus the least massive H/He-dominated gas giant planet found to date. This record was previously held by Saturn.
Gaia Early Data Release 3 Harrison, D L; Breedt, E; Wevers, T ...
Astronomy & astrophysics,
08/2021, Letnik:
652
Journal Article
Recenzirano
Odprti dostop
Context. Since July 2014, the Gaia mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky. Aims. We present the ...Gaia Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by Gaia. Methods. We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to Gaia and (2) Gaia sources which have undergone a significant brightening or fading. Validation of the Gaia transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours. Results. We show that the Gaia Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae, CE = 0.46, is dominated by the Gaia scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is CI = 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec. Conclusions. The per-transit photometry for Gaia transients is precise to 1% at G = 13, and 3% at G = 19. The per-transit astrometry is accurate to 55 mas when compared to Gaia DR2. The Gaia Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge.
We present a survey of the early evolution of 12 Type IIn supernovae (SNe IIn) at ultraviolet and visible light wavelengths. We use this survey to constrain the geometry of the circumstellar material ...(CSM) surrounding SN IIn explosions, which may shed light on their progenitor diversity. In order to distinguish between aspherical and spherical CSM, we estimate the blackbody radius temporal evolution of the SNe IIn of our sample, following the method introduced by Soumagnac et al. We find that higher-luminosity objects tend to show evidence for aspherical CSM. Depending on whether this correlation is due to physical reasons or to some selection bias, we derive a lower limit between 35% and 66% for the fraction of SNe IIn showing evidence for aspherical CSM. This result suggests that asphericity of the CSM surrounding SNe IIn is common-consistent with data from resolved images of stars undergoing considerable mass loss. It should be taken into account for more realistic modeling of these events.
Star formation theory predicts that short-period M-dwarf binaries with highly unequal-mass components are rare. First, the mass ratio of close binary systems is driven to unity due to the secondary ...preferentially accreting gas with high angular momentum. Secondly, both dynamical decay of multiple systems and interactions with tertiary stars that tighten the binary orbit will eject the lowest mass member. Generally, only the two most massive stars are paired after such interactions, and the frequency of tight unequal-mass binaries is expected to decrease steeply with primary mass. In this paper, we present the discovery of a highly unequal-mass eclipsing M-dwarf binary, providing a unique constraint on binary star formation theory and on evolutionary models for low-mass binary stars. The binary is discovered using high-precision infrared light curves from the United Kingdom Infrared Telescope (UKIRT) Wide Field Camera (WFCAM) Transit Survey and has an orbital period of 2.44 d. We find stellar masses of M
1 = 0.53(±0.02) M and M
2 = 0.143(±0.006) M (mass ratio 0.27), and radii of R
1 = 0.51(±0.01) R and R
2 = 0.174(±0.006) R. This puts the companion in a very sparsely sampled and important late M-dwarf mass regime. Since both stars will share the same age and metallicity and straddle the theoretical boundary between fully and partially convective stellar interiors, a comparison can be made to model predictions over a large range of M-dwarf masses using the same model isochrone. Both stars appear to have a slightly inflated radius compared to 1 Gyr` model predictions for their masses, but future work is needed to properly account for the effects of star spots on the light-curve solution. A significant, subsynchronous, ∼2.56 d signal with ∼2 per cent peak-to-peak amplitude is detected in the WFCAM light curve, which we attribute to rotational modulation of cool star spots. We propose that the subsynchronous rotation is either due to a stable star-spot complex at high latitude on the (magnetically active) primary (i.e. differential rotation), or additional magnetic braking, or interaction of the binary with a third body or circumbinary disc during its pre-main-sequence phase.
Abstract
We report on the discovery of four ultra-short-period (P ≤ 0.18 d) eclipsing M-dwarf binaries in the Wide-Field Camera (WFCAM) Transit Survey. Their orbital periods are significantly shorter ...than that of any other known main-sequence binary system, and are all significantly below the sharp period cut-off at P ∼ 0.22 d as seen in binaries of earlier-type stars. The shortest-period binary consists of two M4-type stars in a P = 0.112 d orbit. The binaries are discovered as part of an extensive search for short-period eclipsing systems in over 260 000 stellar light curves, including over 10 000 M-dwarfs down to J = 18 mag, yielding 25 binaries with P ≤ 0.23 d. In a popular paradigm, the evolution of short-period binaries of cool main-sequence stars is driven by the loss of angular momentum through magnetized winds. In this scheme, the observed P ∼ 0.22 d period cut-off is explained as being due to time-scales that are too long for lower-mass binaries to decay into tighter orbits. Our discovery of low-mass binaries with significantly shorter orbits implies that either these time-scales have been overestimated for M-dwarfs, e.g. due to a higher effective magnetic activity, or the mechanism for forming these tight M-dwarf binaries is different from that of earlier-type main-sequence stars.
In the ongoing HATNet survey we have detected a giant planet, with radius 1.33 plus or minus 0.06 R sub(Jup) and mass 1.06 plus or minus 0.12 M sub(Jup), transiting the bright (V = 10.5) star GSC ...03239-00992. The planet is in a circular orbit with period 3.852985 plus or minus 0.000005 days and midtransit epoch 2,454,035.67575 plus or minus 0.00028 (HJD). The parent star is a late F star with mass 1.29 plus or minus 0.06 M unk, radius 1.46 plus or minus 0.06 R unk, T sub(off) similar to 6570 plus or minus 80 K, Fe/H = -0.13 plus or minus 0.08, and age similar to 2.3 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(5) sub(7) Gyr. With this radius and mass, HAT-P-6b has somewhat larger radius than theoretically expected. We describe the observations and their analysis to determine physical properties of the HAT-P-6 system, and briefly discuss some implications of this finding.
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