31 research outputs found
Variability of young stars: Determination of rotational periods of weak-line T Tauri stars in the Cepheus-Cassiopeia star-forming region
We report on observation and determination of rotational periods of ten
weak-line T Tauri stars in the Cepheus-Cassiopeia star-forming region.
Observations were carried out with the Cassegrain-Teleskop-Kamera (CTK) at
University Observatory Jena between 2007 June and 2008 May. The periods
obtained range between 0.49 d and 5.7 d, typical for weak-line and post T Tauri
stars.Comment: 11 pages, 26 figures, accepted to be published in A
Observations of the transiting planet TrES-2 with the AIU Jena telescope in Großschwabhausen
We have started high precision photometric monitoring observations at the AIU Jena observatory in Großschwabhausen near Jena in fall 2006. We used a 25.4cm Cassegrain telescope equipped with a CCD-camera mounted piggyback on a 90cm telescope. To test the attainable photometric precision, we observed stars with known transiting planets. We could recover all planetary transits observed by us. We observed the parent star of the transiting planet TrES-2 over a longer period in Großschwabhausen. Between March and November 2007 seven different transits and almost a complete orbital period were analyzed. Overall, in 31 nights of observation 3423 exposures (in total 57.05h of observation) of the TrES-2 parent star were taken. Here, we present our methods and the resulting light curves. Using our observations we could improve the orbital parameters of the syste
Constraining the reflective properties of WASP-178b using Cheops photometry
Multiwavelength photometry of the secondary eclipses of extrasolar planets is
able to disentangle the reflected and thermally emitted light radiated from the
planetary dayside. This leads to the measurement of the planetary geometric
albedo , which is an indicator of the presence of clouds in the
atmosphere, and the recirculation efficiency , which quantifies the
energy transport within the atmosphere. In this work we aim to measure
and for the planet WASP-178 b, a highly irradiated giant planet with
an estimated equilibrium temperature of 2450 K.} We analyzed archival spectra
and the light curves collected by Cheops and Tess to characterize the host
WASP-178, refine the ephemeris of the system and measure the eclipse depth in
the passbands of the two respective telescopes. We measured a marginally
significant eclipse depth of 7040 ppm in the Tess passband and
statistically significant depth of 7020 ppm in the Cheops passband.
Combining the eclipse depth measurement in the Cheops (lambda_eff=6300 AA) and
Tess (lambda_eff=8000 AA) passbands we constrained the dayside brightness
temperature of WASP-178 b in the 2250-2800 K interval. The geometric albedo
0.1<<0.35 is in general agreement with the picture of poorly
reflective giant planets, while the recirculation efficiency 0.7
makes WASP-178 b an interesting laboratory to test the current heat
recirculation models.Comment: Accepted by Astronomy and Astrophysics on 31/08/202
Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley
TOI-732 is an M dwarf hosting two transiting planets that are located on the
two opposite sides of the radius valley. By doubling the number of available
space-based observations and increasing the number of radial velocity (RV)
measurements, we aim at refining the parameters of TOI-732 b and c. We also use
the results to study the slope of the radius valley and the density valley for
a well-characterised sample of M-dwarf exoplanets. We performed a global MCMC
analysis by jointly modelling ground-based light curves and CHEOPS and TESS
observations, along with RV time series both taken from the literature and
obtained with the MAROON-X spectrograph. The slopes of the M-dwarf valleys were
quantified via a Support Vector Machine (SVM) procedure. TOI-732 b is an
ultrashort-period planet ( d) with a radius
and a mass
(mean density g cm), while the
outer planet at d has ,
, and thus
g cm. Also taking into account our interior structure calculations,
TOI-732 b is a super-Earth and TOI-732 c is a mini-Neptune. Following the SVM
approach, we quantified
,
which is flatter than for Sun-like stars. In line with former analyses, we note
that the radius valley for M-dwarf planets is more densely populated, and we
further quantify the slope of the density valley as
.
Compared to FGK stars, the weaker dependence of the position of the radius
valley on the orbital period might indicate that the formation shapes the
radius valley around M dwarfs more strongly than the evolution mechanisms.Comment: 28 pages (17 in the main text), 18 figures (9 in the main text), 11
tables (7 in the main text). Accepted for publication in A&
CHEOPS observations of KELT-20 b/MASCARA-2 b: An aligned orbit and signs of variability from a reflective dayside
Occultations are windows of opportunity to indirectly peek into the dayside
atmosphere of exoplanets. High-precision transit events provide information on
the spin-orbit alignment of exoplanets around fast-rotating hosts. We aim to
precisely measure the planetary radius and geometric albedo of the ultra-hot
Jupiter (UHJ) KELT-20 b as well as the system's spin-orbit alignment. We
obtained optical high-precision transits and occultations of KELT-20 b using
CHEOPS observations in conjunction with the simultaneous TESS observations. We
interpreted the occultation measurements together with archival infrared
observations to measure the planetary geometric albedo and dayside
temperatures. We further used the host star's gravity-darkened nature to
measure the system's obliquity. We present a time-averaged precise occultation
depth of 82(6) ppm measured with seven CHEOPS visits and 131(+8/-7) ppm from
the analysis of all available TESS photometry. Using these measurements, we
precisely constrain the geometric albedo of KELT-20 b to 0.26(0.04) and the
brightness temperature of the dayside hemisphere to 2566(+77/-80) K. Assuming
Lambertian scattering law, we constrain the Bond albedo to 0.36(+0.04/-0.05)
along with a minimal heat transfer to the night side. Furthermore, using five
transit observations we provide stricter constraints of 3.9(1.1) degrees on the
sky-projected obliquity of the system. The aligned orbit of KELT-20 b is in
contrast to previous CHEOPS studies that have found strongly inclined orbits
for planets orbiting other A-type stars. The comparably high planetary
geometric albedo of KELT-20 b corroborates a known trend of strongly irradiated
planets being more reflective. Finally, we tentatively detect signs of temporal
variability in the occultation depths, which might indicate variable cloud
cover advecting onto the planetary day side.Comment: 27 pages, 15 figures, Accepted for publication in Astronomy &
Astrophysic
The EBLM Project XI. Mass, radius and effective temperature measurements for 23 M-dwarf companions to solar-type stars observed with CHEOPS
Observations of low-mass stars have frequently shown a disagreement between observed stellar radii and radii predicted by theoretical stellar structure models. This ``radius inflation'' problem could have an impact on both stellar and exoplanetary science. We present the final results of our observation programme with the CHEOPS satellite to obtain high-precision light curves of eclipsing binaries with low mass stellar companions (EBLMs). Combined with the spectroscopic orbits of the solar-type companion, we can derive the masses, radii and effective temperatures of 23 M-dwarf stars. We use the PYCHEOPS data analysis software to analyse their primary and secondary occultations. For all but one target, we also perform analyses with TESS light curves for comparison. We have assessed the impact of starspot-induced variation on our derived parameters and account for this in our radius and effective temperature uncertainties using simulated light curves. We observe trends for inflation with both metallicity and orbital separation. We also observe a strong trend in the difference between theoretical and observational effective temperatures with metallicity. There is no such trend with orbital separation. These results are not consistent with the idea that observed inflation in stellar radius combines with lower effective temperature to preserve the luminosity predicted by low-mass stellar models. Our EBLM systems are high-quality and homogeneous measurements that can be used in further studies into radius inflation
A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067
Planets with radii between that of the Earth and Neptune (hereafter referred
to as sub-Neptunes) are found in close-in orbits around more than half of all
Sun-like stars. Yet, their composition, formation, and evolution remain poorly
understood. The study of multi-planetary systems offers an opportunity to
investigate the outcomes of planet formation and evolution while controlling
for initial conditions and environment. Those in resonance (with their orbital
periods related by a ratio of small integers) are particularly valuable because
they imply a system architecture practically unchanged since its birth. Here,
we present the observations of six transiting planets around the bright nearby
star HD 110067. We find that the planets follow a chain of resonant orbits. A
dynamical study of the innermost planet triplet allowed the prediction and
later confirmation of the orbits of the rest of the planets in the system. The
six planets are found to be sub-Neptunes with radii ranging from 1.94 to 2.85
Re. Three of the planets have measured masses, yielding low bulk densities that
suggest the presence of large hydrogen-dominated atmospheres.Comment: Published in Nature on November 30, 2023. Supplementary Information
can be found in the online version of the paper in the journa
A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067
Funding: A.C.Ca. and T.G.Wi. acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. O.Ba. acknowledges that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 865624). M.La. acknowledges funding from a UKRI Future Leader Fellowship, grant number MR/S035214/1. A.Br. was supported by the SNSA. Contributions at the Mullard Space Science Laboratory by E.M.Br. were supported by STFC through the consolidated grant ST/W001136/1. A.Br. was supported by the SNSA. Contributions at the Mullard Space Science Laboratory by E.M.Br. were supported by STFC through the consolidated grant ST/W001136/1. Ch.He. acknowledges support from the European Union H2020-MSCA-ITN-2019 under Grant Agreement no. 860470 (CHAMELEON).Planets with radii between that of the Earth and Neptune (hereafter referred to as 'sub-Neptunes') are found in close-in orbits around more than half of all Sun-like stars . However, their composition, formation and evolution remain poorly understood . The study of multiplanetary systems offers an opportunity to investigate the outcomes of planet formation and evolution while controlling for initial conditions and environment. Those in resonance (with their orbital periods related by a ratio of small integers) are particularly valuable because they imply a system architecture practically unchanged since its birth. Here we present the observations of six transiting planets around the bright nearby star HD 110067. We find that the planets follow a chain of resonant orbits. A dynamical study of the innermost planet triplet allowed the prediction and later confirmation of the orbits of the rest of the planets in the system. The six planets are found to be sub-Neptunes with radii ranging from 1.94R to 2.85R . Three of the planets have measured masses, yielding low bulk densities that suggest the presence of large hydrogen-dominated atmospheres.PostprintPeer reviewe