125 research outputs found
Physical properties, starspot activity, orbital obliquity, and transmission spectrum of the Qatar-2 planetary system from multi-colour photometry
We present seventeen high-precision light curves of five transits of the
planet Qatar-2b, obtained from four defocussed 2m-class telescopes. Three of
the transits were observed simultaneously in the SDSS griz passbands using the
seven-beam GROND imager on the MPG/ESO 2.2-m telescope. A fourth was observed
simultaneously in Gunn grz using the CAHA 2.2-m telescope with BUSCA, and in r
using the Cassini 1.52-m telescope. Every light curve shows small anomalies due
to the passage of the planetary shadow over a cool spot on the surface of the
host star. We fit the light curves with the prism+gemc model to obtain the
photometric parameters of the system and the position, size and contrast of
each spot. We use these photometric parameters and published spectroscopic
measurements to obtain the physical properties of the system to high precision,
finding a larger radius and lower density for both star and planet than
previously thought. By tracking the change in position of one starspot between
two transit observations we measure the orbital obliquity of Qatar-2 b to be
4.3 \pm 4.5 degree, strongly indicating an alignment of the stellar spin with
the orbit of the planet. We calculate the rotation period and velocity of the
cool host star to be 11.4 \pm 0.5 d and 3.28 \pm 0.13 km/s at a colatitude of
74 degree. We assemble the planet's transmission spectrum over the 386-976 nm
wavelength range and search for variations of the measured radius of Qatar-2 b
as a function of wavelength. Our analysis highlights a possible H2/He Rayleigh
scattering in the blue.Comment: 20 pages, 14 figures, to appear in Monthly Notices of the Royal
Astronomical Societ
First observations and magnitude measurement of Starlink's Darksat
Measure the Sloan g' magnitudes of the Starlink's STARLINK-1130 (Darksat) and
1113 LEO communication satellites and determine the effectiveness of the
Darksat darkening treatment at 475.4\,nm. Two observations of the Starlink's
Darksat LEO communication satellite were conducted on 2020/02/08 and 2020/03/06
using a Sloan r' and g' filter respectively. While a second satellite,
STARLINK-1113 was observed on 2020/03/06 using a Sloan g' filter. The initial
observation on 2020/02/08 was a test observation when Darksat was still
manoeuvring to its nominal orbit and orientation. Based on the successful test
observation, the first main observation was conducted on 2020/03/06 along with
an observation of the second Starlink satellite. The calibration, image
processing and analysis of the Darksat Sloan g' image gives an estimated Sloan
g' magnitude of at a range of 976.50\,km. For STARLINK-1113 an
estimated Sloan g' magnitude of at a range of 941.62\,km was
found. When scaled to a range of 550\,km and corrected for the solar and
observer phase angles, a reduction by a factor of two is seen in the reflected
solar flux between Darksat and STARLINK-1113. The data and results presented in
this work, show that the special darkening coating used by Starlink for Darksat
has darkened the Sloan g' magnitude by \,mag, when the range is
equal to a nominal orbital height (550\,km). This result will serve members of
the astronomical community modelling the satellite mega-constellations, to
ascertain their true impact on both the amateur and professional astronomical
communities. Concurrent and further observations are planned to cover the full
optical and NIR spectrum, from an ensemble of instruments, telescopes and
observatories.Comment: Accepted for publication in A&A Letters. 5 pages, 2 figures and 4
table
Physical properties and radius variations in the HAT-P-5 planetary system from simultaneous four-colour photometry
The radii of giant planets, as measured from transit observations, may vary
with wavelength due to Rayleigh scattering or variations in opacity. Such an
effect is predicted to be large enough to detect using ground-based
observations at multiple wavelengths. We present defocussed photometry of a
transit in the HAT-P-5 system, obtained simultaneously through Stromgren u,
Gunn g and r, and Johnson I filters. Two more transit events were observed
through a Gunn r filter. We detect a substantially larger planetary radius in
u, but the effect is greater than predicted using theoretical model atmospheres
of gaseous planets. This phenomenon is most likely to be due to systematic
errors present in the u-band photometry, stemming from variations in the
transparency of Earth's atmosphere at these short wavelengths. We use our data
to calculate an improved orbital ephemeris and to refine the measured physical
properties of the system. The planet HAT-P-5b has a mass of 1.06 +/- 0.11 +/-
0.01 Mjup and a radius of 1.252 +/- 0.042 +/- 0.008 Rjup (statistical and
systematic errors respectively), making it slightly larger than expected
according to standard models of coreless gas-giant planets. Its equilibrium
temperature of 1517 +/- 29 K is within 60K of that of the extensively-studied
planet HD 209458b.Comment: Version 2 corrects the accidental omission of one author in the arXiv
metadata. Accepted for publication in MNRAS. 9 pages, 4 figures, 7 tables.
The properties of HAT-P-5 have been added to the Transiting Extrasolar Planet
Catalogue at http://www.astro.keele.ac.uk/~jkt/tepcat
Physical properties of the WASP-44 planetary system from simultaneous multi-colour photometry
We present ground-based broad-band photometry of two transits in the WASP-44
planetary system obtained simultaneously through four optical (Sloan g', r',
i', z') and three near-infrared (NIR; J, H, K) filters. We achieved low
scatters of 1-2 mmag per observation in the optical bands with a cadence of 48
s, but the NIR-band light curves present much greater scatter. We also observed
another transit of WASP-44 b by using a Gunn-r filter and telescope
defocussing, with a scatter of 0.37 mmag per point and an observing cadence
around 135 s. We used these data to improve measurements of the time of
mid-transit and the physical properties of the system. In particular, we
improved the radius measurements of the star and planet by factors of 3 and 4,
respectively. We find that the radius of WASP-44 b is 1.002 R_Jup, which is
slightly smaller than previously thought and differs from that expected for a
core-free planet. In addition, with the help of a synthetic spectrum, we
investigated the theoretically-predicted variation of the planetary radius as a
function of wavelength, covering the range 370-2440 nm. We can rule out extreme
variations at optical wavelengths, but unfortunately our data are not precise
enough (especially in the NIR bands) to differentiate between the theoretical
spectrum and a radius which does not change with wavelength.Comment: 13 pages, 6 figures, to appear in Monthly Notices of the Royal
Astronomical Societ
- A tool for multiband light curve modeling of planetary transits and stellar spots
Several studies have shown that stellar activity features, such as occulted
and non-occulted starspots, can affect the measurement of transit parameters
biasing studies of transit timing variations and transmission spectra. We
present , which we designed to model multiband transit
light curves showing starspot anomalies, inferring both transit and spot
parameters. The code follows a pixellation approach to model the star with its
corresponding limb darkening, spots, and transiting planet on a two dimensional
Cartesian coordinate grid. We combine with an MCMC
framework to study and derive exoplanet transmission spectra, which provides
statistically robust values for the physical properties and uncertainties of a
transiting star-planet system. We validate 's performance
by analyzing eleven synthetic light curves of four different star-planet
systems and 20 transit light curves of the well-studied WASP-41b system. We
also investigate the impact of starspots on transit parameters and derive
wavelength dependent transit depth values for WASP-41b covering a range of
6200-9200 , indicating a flat transmission spectrum.Comment: 17 pages, 22 figures; accepted for publication in Astronomy &
Astrophysic
Erratum: Physical properties, star-spot activity, orbital obliquity and transmission spectrum of the Qatar-2 planetary system from multicolour photometry
Optical-to-NIR magnitude measurements of the Starlink LEO Darksat satellite and effectiveness of the darkening treatment
Four observations of Starlink's LEO communication satellites, Darksat and
STARLINK-1113, were conducted on two nights with two telescopes. The Chakana
0.6\,m telescope at the Ckoirama observatory (Chile) observed both satellites
on 5\,Mar\,2020 (UTC) and 7\,Mar\,2020 (UTC) using a Sloan r' and Sloan i'
filter, respectively. The ESO VISTA 4.1\,m telescope with the VIRCAM instrument
observed both satellites on 5\,Mar\,2020 (UTC) and 7\,Mar\,2020 (UTC) in the
NIR J-band and Ks-band, respectively. The calibration, image processing, and
analysis of the Darksat images give r\,\,5.6\,mag,
i\,\,5.0\,mag, J\,\,4.2\,mag, and Ks\,\,4.0\,mag
when scaled to a range of 550\,km (airmass ) and corrected for the solar
incidence and observer phase angles. In comparison, the STARLINK-1113 images
give r\,\,4.9\,mag, i\,\,4.4\,mag, J\,\,3.8\,mag,
and Ks\,\,3.6\,mag when corrected for range, solar incidence, and
observer phase angles. The data and results presented in this work show that
the special darkening coating used by Starlink for Darksat has darkened the
Sloan r' magnitude by 50\,\%, Sloan i' magnitude by 42\,\%, NIR J magnitude by
32\,\%, and NIR Ks magnitude by 28\,\%. The results show that both satellites
increase in reflective brightness with increasing wavelength and that the
effectiveness of the darkening treatment is reduced at longer wavelengths. This
shows that the mitigation strategies being developed by Starlink and other LEO
satellite operators need to take into account other wavelengths, not just the
optical. This work highlights the continued importance of obtaining
multi-wavelength observations of many different LEO satellites in order to
characterise their reflective properties and to aid the community in developing
impact simulations and developing mitigation tools.Comment: Accepted for publication in A&A, 10 pages, 10 figures, 3 table
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