We report on the discovery of HAT-P-11b, the smallest radius transiting extrasolar planet (TEP) discovered from the ground, and the first hot Neptune discovered to date by transit searches. HAT-P-11b ...orbits the bright (V = 9.587) and metal rich (Fe/H = +0.31 +- 0.05) K4 dwarf star GSC 03561-02092 with P = 4.8878162 +- 0.0000071 days and produces a transit signal with depth of 4.2 mmag, the shallowest found by transit searches that is due to a confirmed planet. We present a global analysis of the available photometric and radial velocity (RV) data that result in stellar and planetary parameters, with simultaneous treatment of systematic variations. The planet, like its near-twin GJ 436b, is somewhat larger than Neptune (17 M{sub +}, 3.8 R{sub +}) both in mass M{sub p} = 0.081 +- 0.009 M{sub J}(25.8 +- 2.9 M{sub +}) and radius R{sub p} = 0.422 +- 0.014 R{sub J}(4.73 +- 0.16 R{sub +}). HAT-P-11b orbits in an eccentric orbit with e = 0.198 +- 0.046 and omega = 355.{sup 0}2 +- 17.{sup 0}3, causing a reflex motion of its parent star with amplitude 11.6 +- 1.2 m s{sup -1}, a challenging detection due to the high level of chromospheric activity of the parent star. Our ephemeris for the transit events is T{sub c} = 2454605.89132 +- 0.00032 (BJD), with duration 0.0957 +- 0.0012 days, and secondary eclipse epoch of 2454608.96 +- 0.15 days (BJD). The basic stellar parameters of the host star are M{sub *} = 0.809{sup +0.020}{sub -0.027} M{sub sun}, R{sub *} = 0.752 +- 0.021 R{sub sun}, and T{sub eff*} = 4780 +- 50 K. Importantly, HAT-P-11 will lie on one of the detectors of the forthcoming Kepler mission; this should make possible fruitful investigations of the detailed physical characteristic of both the planet and its parent star at unprecedented precision. We discuss an interesting constraint on the eccentricity of the system by the transit light curve and stellar parameters. This will be particularly useful for eccentric TEPs with low-amplitude RV variations in Kepler's field. We also present a blend analysis, that for the first time treats the case of a blended transiting hot Jupiter mimicking a transiting hot Neptune, and proves that HAT-P-11b is not such a blend.
Using light curves from the HATNet survey for transiting extrasolar planets we investigate the optical broadband photometric variability of a sample of 27, 560 field K and M dwarfs selected by color ...and proper motion (V -- K 3.0, Delta *m > 30 mas yr--1, plus additional cuts in J -- H versus H -- KS and on the reduced proper motion). We search the light curves for periodic variations and for large-amplitude, long-duration flare events. A total of 2120 stars exhibit potential variability, including 95 stars with eclipses and 60 stars with flares. Based on a visual inspection of these light curves and an automated blending classification, we select 1568 stars, including 78 eclipsing binaries (EBs), as secure variable star detections that are not obvious blends. We estimate that a further ~26% of these stars may be blends with fainter variables, though most of these blends are likely to be among the hotter stars in our sample. We find that only 38 of the 1568 stars, including five of the EBs, have previously been identified as variables or are blended with previously identified variables. One of the newly identified EBs is 1RXS J154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, for which we derive preliminary estimates for the component masses and radii of M 1 = M 2 = 0.258 ? 0.008 M and R 1 = R 2 = 0.289 ? 0.007 R . The radii of the component stars are larger than theoretical expectations if the system is older than ~200 Myr. The majority of the variables are heavily spotted BY Dra-type stars for which we determine rotation periods. Using this sample, we investigate the relations between period, color, age, and activity measures, including optical flaring, for K and M dwarfs, finding that many of the well-established relations for F, G, and K dwarfs continue into the M dwarf regime. We find that the fraction of stars that is variable with peak-to-peak amplitudes greater than 0.01 mag increases exponentially with the V -- KS color such that approximately half of field dwarfs in the solar neighborhood with M 0.2 M are variable at this level. Our data hint at a change in the rotation-activity-age connection for stars with M 0.25 M .
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 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.
We report on the discovery of a planetary system with a close-in transiting hot Jupiter on a near circular orbit and a massive outer planet on a highly eccentric orbit. The inner planet, HAT-P-13b, ...transits the bright V = 10.622 G4 dwarf star GSC 3416 - 00543 every P = 2.916260 +/- 0.000010 days, with transit epoch Tc = 2454779.92979 +/- 0.00038 (BJD) and duration 0.1345 +/- 0.0017 days. The outer planet HAT-P-13c orbits the star every P 2 = 428.5 +/- 3.0 days with a nominal transit center (assuming zero impact parameter) of T 2c = 2454870.4 +/- 1.8 (BJD) or time of periastron passage T 2,peri = 2454890.05 +/- 0.48 (BJD). Transits of the outer planet have not been observed, and may not be present. The host star has a mass of 1.22+0.05 -0.10 M, radius of 1.56 +/- 0.08 R, effective temperature of 5653 +/- 90 K, and is rather metal-rich with Fe/H = +0.41 +/- 0.08. The inner planetary companion has a mass of 0.853+0.029 -0.046 M J, and radius of 1.281 +/- 0.079 R J, yielding a mean density of 0.498+0.103 -0.069 g cm-3. The outer companion has m 2sin i 2 = 15.2 +/- 1.0 M J, and orbits on a highly eccentric orbit of e 2 = 0.691 +/- 0.018. While we have not detected significant transit timing variations of HAT-P-13b, due to gravitational and light-travel time effects, future observations will constrain the orbital inclination of HAT-P-13c, along with its mutual inclination to HAT-P-13b. The HAT-P-13 (b, c) double-planet system may prove extremely valuable for theoretical studies of the formation and dynamics of planetary systems.
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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