69 research outputs found
Reaching the boundary between stellar kinematic groups and very wide binaries. III. Sixteen new stars and eight new wide systems in the beta Pictoris moving group
Aims. We look for common proper motion companions to stars of the nearby
young beta Pictoris moving group. Methods. First, we compiled a list of 185
beta Pictoris members and candidate members from 35 representative works. Next,
we used the Aladin and STILTS virtual observatory tools, and the PPMXL proper
motion and Washington Double Star catalogues to look for companion candidates.
The resulting potential companions were subjects of a dedicated
astro-photometric follow-up using public data from all-sky surveys. After
discarding 67 sources by proper motion and 31 by colour-magnitude diagrams, we
obtained a final list of 36 common proper motion systems. The binding energy of
two of them is perhaps too small to be considered physically bound. Results. Of
the 36 pairs and multiple systems, eight are new, 16 have only one stellar
component previously classified as a beta Pictoris member, and three have
secondaries at or below the hydrogen-burning limit. Sixteen stars are reported
here for the first time as moving group members. The unexpected large number of
high-order multiple systems, 12 triples and two quadruples among 36 systems,
may suggest a biased list of members towards close binaries or an increment of
the high-order-multiple fraction for very wide systems.Comment: A&A in pres
CARMENES input catalogue of M dwarfs II. High-resolution imaging with FastCam
Aims. We search for low-mass companions of M dwarfs and characterize their multiplicity fraction with the purpose of helping in the selection of the most appropriate targets for the CARMENES exoplanet survey. Methods. We obtained high-resolution images in the I band with the lucky imaging instrument FastCam at the 1.5m Telescopio Carlos Sanchez for 490 mid-to late-M dwarfs. For all the detected binaries, we measured angular separations, position angles, and magnitude differences in the I band. We also calculated the masses of each individual component and estimated orbital periods, using the available magnitude and colour relations for M dwarfs and our own M-J-spectral type and mass-M-I relations. To avoid biases in our sample selection, we built a volume-limited sample of M0.0-M5.0 dwarfs that is complete up to 86% within 14 pc. Results. From the 490 observed stars, we detected 80 companions in 76 systems, of which 30 are new discoveries. Another six companion candidates require additional astrometry to confirm physical binding. The multiplicity fraction in our observed sample is 16.7 +/- 2.0%. The bias-corrected multiplicity fraction in our volume-limited sample is 19.5 +/- 2.3% for angular separations of 0.2 to 5.0 arcsec (1.4-65.6 au), with a peak in the distribution of the projected physical separations at 2.5-7.5 au. For M0.0-M3.5V primaries, our search is sensitive to mass ratios higher than 0.3 and there is a higher density of pairs with mass ratios over 0.8 compared to those at lower mass ratios. Binaries with projected physical separations shorter than 50 au also tend to be of equal mass. For 26 of our systems, we estimated orbital periods shorter than 50 a, 10 of which are presented here for the first time. We measured variations in angular separation and position angle that are due to orbital motions in 17 of these systems. The contribution of binaries and multiples with angular separations shorter than 0.2 arcsec, longer than 5.0 arcsec, and of spectroscopic binaries identified from previous searches, although not complete, may increase the multiplicity fraction of M dwarfs in our volume-limited sample to at least 36%
A Search for FeH in Hot-Jupiter Atmospheres with High-Dispersion Spectroscopy
Most of the molecules detected thus far in exoplanet atmospheres, such as
water and CO, are present for a large range of pressures and temperatures. In
contrast, metal hydrides exist in much more specific regimes of parameter
space, and so can be used as probes of atmospheric conditions. Iron hydride
(FeH) is a dominant source of opacity in low-mass stars and brown dwarfs, and
evidence for its existence in exoplanets has recently been observed at low
resolution. We performed a systematic search of archival CARMENES near-infrared
data for signatures of FeH during transits of 12 exoplanets. These planets span
a large range of equilibrium temperatures (600
4000K) and surface gravities (2.5 3.5). We
did not find a statistically significant FeH signal in any of the atmospheres,
but obtained potential low-confidence signals (SNR3) in two planets,
WASP-33b and MASCARA-2b. Previous modeling of exoplanet atmospheres indicate
that the highest volume mixing ratios (VMRs) of 10 to 10 are
expected for temperatures between 1800 and 3000K and log . The two
planets for which we find low-confidence signals are in the regime where strong
FeH absorption is expected. We performed injection and recovery tests for each
planet and determined that FeH would be detected in every planet for VMRs , and could be detected in some planets for VMRs as low as 10.
Additional observations are necessary to conclusively detect FeH and assess its
role in the temperature structures of hot Jupiter atmospheres.Comment: Accepted to AAS journal
CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOS
Context. CARMENES is a stabilised, high-resolution, double-channel
spectrograph at the 3.5 m Calar Alto telescope. It is optimally designed for
radial-velocity surveys of M dwarfs with potentially habitable Earth-mass
planets. Aims. We prepare a list of the brightest, single M dwarfs in each
spectral subtype observable from the northern hemisphere, from which we will
select the best planet-hunting targets for CARMENES. Methods. In this first
paper on the preparation of our input catalogue, we compiled a large amount of
public data and collected low-resolution optical spectroscopy with CAFOS at the
2.2 m Calar Alto telescope for 753 stars. We derived accurate spectral types
using a dense grid of standard stars, a double least-squares minimisation
technique, and 31 spectral indices previously defined by other authors.
Additionally, we quantified surface gravity, metallicity, and chromospheric
activity for all the stars in our sample. Results. We calculated spectral types
for all 753 stars, of which 305 are new and 448 are revised. We measured
pseudo-equivalent widths of Halpha for all the stars in our sample, concluded
that chromospheric activity does not affect spectral typing from our indices,
and tabulated 49 stars that had been reported to be young stars in open
clusters, moving groups, and stellar associations. Of the 753 stars, two are
new subdwarf candidates, three are T Tauri stars, 25 are giants, 44 are K
dwarfs, and 679 are M dwarfs. Many of the 261 investigated dwarfs in the range
M4.0-8.0 V are among the brightest stars known in their spectral subtype.
Conclusions. This collection of low-resolution spectroscopic data serves as a
candidate target list for the CARMENES survey and can be highly valuable for
other radial-velocity surveys of M dwarfs and for studies of cool dwarfs in the
solar neighbourhood.Comment: A&A, in pres
A search for He I airglow emission from the hot Jupiter tau Boo b
The helium absorption line at 10830 {\AA}, originating from the metastable
triplet state 2S, has been suggested as an excellent probe for the extended
atmospheres of hot Jupiters and their hydrodynamic escape processes, and has
recently been detected in the transmission spectra of a handful of planets. The
isotropic re-emission will lead to helium airglow that may be observable at
other orbital phases. The goal of this paper is to investigate the
detectability of He I emission at 10830 {\AA} in the atmospheres of exoplanets
using high-resolution spectroscopy, providing insights into the properties of
the upper atmospheres of close-in gas giants. We estimated the expected
strength of He I emission in hot Jupiters based on their transmission signal.
We searched for the He I 10830 {\AA} emission feature in tau Boo b in three
nights of high-resolution spectra taken by CARMENES at the 3.5m Calar Alto
telescope. The spectra from each night were corrected for telluric absorption,
sky emission lines, and stellar features, and were shifted to the planetary
rest frame to search for the emission. The He I emission is not detected in tau
Boo b, reaching a 5 sigma contrast limit of 410 for emission
line widths above 20 km/s. This is roughly a factor of 8 above the expected
level of emission (assuming a typical He I transit absorption of 1% for hot
Jupiters). This suggests that targeting the He I emission with well-designed
observations using upcoming instruments such as VLT/CRIRES+ and E-ELT/HIRES is
possible.Comment: Accepted for publication in A&A; 9 pages, 9 figure
Ground-based detection of an extended helium atmosphere in the Saturn-mass exoplanet WASP-69b
Hot gas giant exoplanets can lose part of their atmosphere due to strong
stellar irradiation, affecting their physical and chemical evolution. Studies
of atmospheric escape from exoplanets have mostly relied on space-based
observations of the hydrogen Lyman-{\alpha} line in the far ultraviolet which
is strongly affected by interstellar absorption. Using ground-based
high-resolution spectroscopy we detect excess absorption in the helium triplet
at 1083 nm during the transit of the Saturn-mass exoplanet WASP-69b, at a
signal-to-noise ratio of 18. We measure line blue shifts of several km/s and
post transit absorption, which we interpret as the escape of part of the
atmosphere trailing behind the planet in comet-like form.
[Additional notes by authors: Furthermore, we provide upper limits for helium
signals in the atmospheres of the exoplanets HD 209458b, KELT-9b, and GJ 436b.
We investigate the host stars of all planets with detected helium signals and
those of the three planets we derive upper limits for. In each case we
calculate the X-ray and extreme ultraviolet flux received by these planets. We
find that helium is detected in the atmospheres of planets (orbiting the more
active stars and) receiving the larger amount of irradiation from their host
stars.]Comment: Submitted to Science on 14 March 2018; Accepted by Science on 16
November 2018; Published by Science on 6 December 2018. This is the author's
version of the work. It is posted here by permission of the AAAS for personal
use. The definitive version was published in Science, on 6 December 2018 -
Report: pages 21 (preprint), 4 figures - Supplementary materials: 22 pages,
10 figures, 3 table
Detection of He I \AA{} absorption on HD 189733 b with CARMENES high-resolution transmission spectroscopy
We present three transit observations of HD 189733 b obtained with the
high-resolution spectrograph CARMENES at Calar Alto. A strong absorption signal
is detected in the near-infrared He I triplet at 10830 \AA{} in all three
transits. During mid-transit, the mean absorption level is %
measured in a 10 km s range at a net blueshift of km
s (10829.84--10830.57 \AA{}). The absorption signal exhibits radial
velocities of km s and km s during
ingress and egress, respectively; measured in the planetary rest frame. We show
that stellar activity related pseudo-signals interfere with the planetary
atmospheric absorption signal. They could contribute as much as 80% of the
observed signal and might also affect the radial velocity signature, but
pseudo-signals are very unlikely to explain the entire signal. The observed
line ratio between the two unresolved and the third line of the He I triplet is
, which strongly deviates from the value expected for an optically
thin atmospheres. When interpreted in terms of absorption in the planetary
atmosphere, this favors a compact helium atmosphere with an extent of only 0.2
planetary radii and a substantial column density on the order of cm. The observed radial velocities can be understood either in
terms of atmospheric circulation with equatorial superrotation or as a sign of
an asymmetric atmospheric component of evaporating material. We detect no clear
signature of ongoing evaporation, like pre- or post-transit absorption, which
could indicate material beyond the planetary Roche lobe, or radial velocities
in excess of the escape velocity. These findings do not contradict planetary
evaporation, but only show that the detected helium absorption in HD 189733 b
does not trace the atmospheric layers that show pronounced escape signatures.Comment: 13 pages, 12 figures, accepted for publication in A&
Water vapour detection in hot Jupiters with the CARMENES NIR channel
Stars and planetary system
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