523 research outputs found
A new mass and radius determination of the ultra-short period planet K2-106b and the fluffy planet K2-106c
Ultra-short period planets have orbital periods of less than one day. Since their masses and radii can be determined to a higher precision than long-period planets, they are the preferred targets to determine the density of planets which constrains their composition. The K2-106 system is particularly interesting because it contains two planets of nearly identical masses. One is a high density USP, the other is a low-density planet that has an orbital period of 13 days. Combining the Gaia DR3 results with new ESPRESSO data allows us to determine the masses and radii of the two planets more precisely than before. We find that the USP K2-106b has a density consistent with an Earth-like composition, and K2-106c is a low-density planet that presumably has an extended atmosphere. We measure a radius of Rp = 1.676-0.037+0.037 R⊕, a mass of Mp = 7.80-0.70+0.71 M⊕ and a density of ρ = 9.09-0.98+0.98 gcm-3 for K2-106b. For K2-106c, we derive Rp = 2.84-0.08+0.10 R⊕, Mp = 7.3-2.4+2.5 M⊕, and a density of ρ = 1.72-0.58+0.66 gcm-3. We finally discuss the possible structures of the two planets with respect to other low-mass planets
Search for an exosphere in sodium and calcium in the transmission spectrum of exoplanet 55 Cancri e
[Abridged] The aim of this work is to search for an absorption signal from
exospheric sodium (Na) and singly ionized calcium (Ca) in the optical
transmission spectrum of the hot rocky super-Earth 55 Cancri e. Although the
current best-fitting models to the planet mass and radius require a possible
atmospheric component, uncertainties in the radius exist, making it possible
that 55 Cancri e could be a hot rocky planet without an atmosphere. High
resolution (R110000) time-series spectra of five transits of 55 Cancri e,
obtained with three different telescopes (UVES/VLT, HARPS/ESO 3.6m &
HARPS-N/TNG) were analysed. Targeting the sodium D lines and the calcium H and
K lines, the potential planet exospheric signal was filtered out from the much
stronger stellar and telluric signals, making use of the change of the radial
component of the orbital velocity of the planet over the transit from -57 to
+57 km/sec. Combining all five transit data sets, we detect a signal
potentially associated with sodium in the planet exosphere at a statistical
significance level of 3. Combining the four HARPS transits that cover
the calcium H and K lines, we also find a potential signal from ionized calcium
(4.1 ). Interestingly, this latter signal originates from just one of
the transit measurements - with a 4.9 detection at this epoch.
Unfortunately, due to the low significance of the measured sodium signal and
the potentially variable Ca signal, we estimate the p-values of these
signals to be too high (corresponding to <4) to claim unambiguous
exospheric detections. By comparing the observed signals with artificial
signals injected early in the analysis, the absorption by Na and Ca are
estimated to be at a level of approximately 2.3 and 7.0 respectively, relative to the stellar spectrum.Comment: 15 pages, 8 figures, submission updated after English language
editing, submission updated to correct a mistaken cross-reference noticed in
A&A proo
Incidence of debris discs around FGK stars in the solar neighbourhood
Debris discs are a consequence of the planet formation process and constitute
the fingerprints of planetesimal systems. Their solar system's counterparts are
the asteroid and Edgeworth-Kuiper belts. The aim of this paper is to provide
robust numbers for the incidence of debris discs around FGK stars in the solar
neighbourhood. The full sample of 177 FGK stars with d<20 pc proposed for the
DUNES survey is presented. Herschel/PACS observations at 100 and 160 micron
complemented with data at 70 micron, and at 250, 350 and 500 micron SPIRE
photometry, were obtained. The 123 objects observed by the DUNES collaboration
were presented in a previous paper. The remaining 54 stars, shared with the
DEBRIS consortium and observed by them, and the combined full sample are
studied in this paper. The incidence of debris discs per spectral type is
analysed and put into context together with other parameters of the sample,
like metallicity, rotation and activity, and age.
The subsample of 105 stars with d<15 pc containing 23 F, 33 G and 49 K stars,
is complete for F stars, almost complete for G stars and contains a substantial
number of K stars to draw solid conclusions on objects of this spectral type.
The incidence rates of debris discs per spectral type 0.26 (6 objects with
excesses out of 23 F stars), 0.21 (7 out of 33 G stars) and 0.20 (10 out of 49
K stars), the fraction for all three spectral types together being 0.22 (23 out
of 105 stars). Uncertainties corresponding to a 95% confidence level are given
in the text for all these numbers. The medians of the upper limits of
L_dust/L_* for each spectral type are 7.8E-7 (F), 1.4E-6 (G) and 2.2E-6 (K);
the lowest values being around 4.0E-7. The incidence of debris discs is similar
for active (young) and inactive (old) stars. The fractional luminosity tends to
drop with increasing age, as expected from collisional erosion of the debris
belts.Comment: 31 pages, 15 figures, 10 tables, 2 appendice
High angular resolution imaging and infrared spectroscopy of CoRoT candidates
Studies of transiting extrasolar planets are of key importance for
understanding the nature of planets outside our solar system because their
masses, diameters, and bulk densities can be measured. An important part of
transit-search programmes is the removal of false-positives. The critical
question is how many of the candidates that passed all previous tests are false
positives. For our study we selected 25 CoRoT candidates that have already been
screened against false-positives using detailed analysis of the light curves
and seeing-limited imaging, which has transits that are between 0.7 and 0.05%
deep. We observed 20 candidates with the adaptive optics imager NaCo and 18
with the high-resolution infrared spectrograph CRIRES. We found previously
unknown stars within 2 arcsec of the targets in seven of the candidates. All of
these are too faint and too close to the targets to have been previously
detected with seeing-limited telescopes in the optical. Our study thus leads to
the surprising results that if we remove all candidates excluded by the
sophisticated analysis of the light-curve, as well as carrying out deep imaging
with seeing-limited telescopes, still 28-35% of the remaining candidates are
found to possess companions that are bright enough to be false-positives. Given
that the companion-candidates cluster around the targets and that the J-K
colours are consistent with physical companions, we conclude that the
companion-candidates are more likely to be physical companions rather than
unrelated field stars.Comment: 12 pages, 12 figures, A&A in pres
Do we Need to Solve the Exozodi Question? If Yes, How to Best Solve It?
When observing an extrasolar planetary system, the most luminous component after the star itself is generally the light scattered and/or thermally emitted by a population of micron-sized dust grains. These grains are expected to be continuously replenished by the collisions and evaporation of larger bodies just as in our solar zodiacal cloud. Exozodiacal clouds (“exozodis”) must therefore be seriously taken into account when attempting to directly image faint Earth-like planets (exoEarths, for short). This paper summarizes the oral contributions and discussions that took place during the Satellite Meeting on exozodiacal dust disks, in an attempt to address the following two questions: Do we need to solve the exozodi question? If yes, how to best solve it
Doppler tomography of transiting exoplanets: A prograde, low-inclined orbit for the hot Jupiter CoRoT-11b
We report the detection of the Doppler shadow of the transiting hot Jupiter
CoRoT-11b. Our analysis is based on line-profile tomography of time-series,
Keck/HIRES high-resolution spectra acquired during the transit of the planet.
We measured a sky-projected, spin-orbit angle of 0.1 +/- 2.6 degrees, which is
consistent with a very low-inclined orbit with respect to the stellar rotation
axis. We refined the physical parameters of the system using a Markov chain
Monte Carlo simultaneous fitting of the available photometric and spectroscopic
data. An analysis of the tidal evolution of the system shows how the currently
measured obliquity and its uncertainty translate into an initial absolute value
of less than about 10 degrees on the zero-age main sequence, for an expected
average modified tidal quality factor of the star Q'* > 4 x 10^6. This is
indicative of an inward migration scenario that would not have perturbed the
primordial low obliquity of CoRoT-11b. Taking into account the effective
temperature and mass of the planet host star (Teff=6440 K, M*=1.23 MSun), the
system can be considered a new telling exception to the recently proposed
trend, according to which relatively hot and massive stars (Teff>6250 K, M*>1.2
MSun) seem to be preferentially orbited by hot Jupiters with high obliquity.Comment: 5 pages, 4 figures, accepted for publication in A&A Letter
The spin-orbit angle of the transiting hot jupiter CoRoT-1b
We measure the angle between the planetary orbit and the stellar rotation
axis in the transiting planetary system CoRoT-1, with new HIRES/Keck and
FORS/VLT high-accuracy photometry. The data indicate a highly tilted system,
with a projected spin-orbit angle lambda = 77 +- 11 degrees. Systematic
uncertainties in the radial velocity data could cause the actual errors to be
larger by an unknown amount, and this result needs to be confirmed with further
high-accuracy spectroscopic transit measurements.
Spin-orbit alignment has now been measured in a dozen extra-solar planetary
systems, and several show strong misalignment. The first three misaligned
planets were all much more massive than Jupiter and followed eccentric orbits.
CoRoT-1, however, is a jovian-mass close-in planet on a circular orbit. If its
strong misalignment is confirmed, it would break this pattern. The high
occurence of misaligned systems for several types of planets and orbits favours
planet-planet scattering as a mechanism to bring gas giants on very close
orbits.Comment: to appear in in MNRAS letters [5 pages
Introduction of HIV-2 and multiple HIV-1 subtypes to Lebanon.
HIV genetic variability, phylogenetic relationships, and transmission dynamics were analyzed in 26 HIV-infected patients from Lebanon. Twenty-five specimens were identified as HIV-1 and one as HIV-2 subtype B. The 25 strains were classified into six env-C2-V3 HIV-1 subtypes: B (n = 10), A (n = 11), C (n = 1), D (n = 1), G (n = 1), and unclassifiable. Potential recombinants combining parts of viral regions from different subtypes Aenv/Dpol/Agag, Genv/Apol, and the unclassifiable-subtype(env)/unclassifiable-subtype(pol)/Agag were found in three patients. Epidemiologic analysis of travel histories and behavioral risks indicated that HIV-1 and HIV-2 subtypes reflected HIV strains prevalent in countries visited by patients or their sex partners. Spread of complex HIV-subtype distribution patterns to regions where HIV is not endemic may be more common than previously thought. Blood screening for both HIV-1 and HIV-2 in Lebanon is recommended to protect the blood supply. HIV subtype data provide information for vaccine development
K2-137 b: an Earth-sized planet in a 4.3-hour orbit around an M-dwarf
We report the discovery from K2 of a transiting terrestrial planet in an
ultra-short-period orbit around an M3-dwarf. K2-137 b completes an orbit in
only 4.3 hours, the second-shortest orbital period of any known planet, just 4
minutes longer than that of KOI 1843.03, which also orbits an M-dwarf. Using a
combination of archival images, AO imaging, RV measurements, and light curve
modelling, we show that no plausible eclipsing binary scenario can explain the
K2 light curve, and thus confirm the planetary nature of the system. The
planet, whose radius we determine to be 0.89 +/- 0.09 Earth radii, and which
must have a iron mass fraction greater than 0.45, orbits a star of mass 0.463
+/- 0.052 Msol and radius 0.442 +/- 0.044 Rsol.Comment: 12 pages, 9 figures, accepted for publication in MNRA
The debris disc of solar analogue Τ Ceti : Herschel observations and dynamical simulations of the proposed multiplanet system
S. M. Lawler, et al, 'The debris disk of solar analogue τ Ceti: Herschel observations and dynamical simulations of the proposed multiplanet system', Monthly Notices of the Royal Astronomical Society, Vol. 444 (3): 2665-2675, first published online 11 September 2014. The version of record is available online at doi: 10.1093/mnras/stu1641 © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.Τ Ceti is a nearby, mature G-type star very similar to our Sun, with a massive Kuiper Belt analogue and possible multiplanet system that has been compared to our Solar system. We present Herschel Space Observatory images of the debris disc, finding the disc is resolved at 70 μm and 160 μm, and marginally resolved at 250 μm. The Herschel images and infrared photometry from the literature are best modelled using a wide dust annulus with an inner edge between 1 and 10 au and an outer edge at~55 au, inclined from face-on by 35° ±10°, and with no significant azimuthal structure. We model the proposed tightly packed planetary system of five super-Earths and find that the innermost dynamically stable disc orbits are consistent with the inner edge found by the observations. The photometric modelling, however, cannot rule out a disc inner edge as close to the star as 1 au, though larger distances produce a better fit to the data. Dynamical modelling shows that the five-planet system is stable with the addition of a Neptune or smaller mass planet on an orbit outside 5 au, where the radial velocity data analysis would not have detected a planet of this mass.Peer reviewe
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