45 research outputs found
Protoplanetary disk lifetimes vs stellar mass and possible implications for giant planet populations
We study the dependence of protoplanetary disk evolution on stellar mass
using a large sample of young stellar objects in nearby young star-forming
regions. We update the protoplanetary disk fractions presented in our recent
work (paper I of this series) derived for 22 nearby (< 500 pc) associations
between 1 and 100 Myr. We use a subsample of 1 428 spectroscopically confirmed
members to study the impact of stellar mass on protoplanetary disk evolution.
We divide this sample into two stellar mass bins (2 M boundary) and
two age bins (3 Myr boundary), and use infrared excesses over the photospheric
emission to classify objects in three groups: protoplanetary disks, evolved
disks, and diskless. The homogeneous analysis and bias corrections allow for a
statistically significant inter-comparison of the obtained results. We find
robust statistical evidence of disk evolution dependence with stellar mass. Our
results, combined with previous studies on disk evolution, confirm that
protoplanetary disks evolve faster and/or earlier around high-mass (> 2
M) stars. We also find a roughly constant level of evolved disks
throughout the whole age and stellar mass spectra. We conclude that
protoplanetary disk evolution depends on stellar mass. Such a dependence could
have important implications for gas giant planet formation and migration, and
could contribute to explaining the apparent paucity of hot Jupiters around
high-mass stars.Comment: Accepted for publication in A&A. 13 pages, 8 figures, 5 table
Herschel/PACS photometry of transiting-planet host stars with candidate warm debris disks
Dust in debris disks is produced by colliding or evaporating planetesimals,
remnants of the planet formation process. Warm dust disks, known by their
emission at < 24 micron, are rare (4% of FGK main sequence stars) and
especially interesting because they trace material in the region likely to host
terrestrial planets, where the dust has a very short dynamical lifetime.
Statistical analyses of the source counts of excesses as found with the mid-IR
Wide Field Infrared Survey Explorer (WISE) suggest that warm-dust candidates
found for the Kepler transiting-planet host-star candidates can be explained by
extragalactic or galactic background emission aligned by chance with the target
stars. These statistical analyses do not exclude the possibility that a given
WISE excess could be due to a transient dust population associated with the
target. Here we report Herschel/PACS 100 and 160 micron follow-up observations
of a sample of Kepler and non-Kepler transiting-planet candidates' host stars,
with candidate WISE warm debris disks, aimed at detecting a possible cold
debris disk in any of them. No clear detections were found in any one of the
objects at either wavelength. Our upper limits confirm that most objects in the
sample do not have a massive debris disk like that in beta Pic. We also show
that the planet-hosting star WASP-33 does not have a debris disk comparable to
the one around eta Crv. Although the data cannot be used to rule out rare warm
disks around the Kepler planet-hosting candidates, the lack of detections and
the characteristics of neighboring emission found at far-IR wavelengths support
an earlier result suggesting that most of the WISE-selected IR excesses around
Kepler candidate host stars are likely due to either chance alignment with
background IR-bright galaxies and/or to interstellar emission.Comment: 8 pages, 3 figures, accepted for publication at Astronomy &
Astrophysics on 4 August 201
Proper motions of young stars in Chamaeleon. I. A Virtual Observatory study of spectroscopically confirmed members
(abridged) We want to provide further evidence of the origin of the proposed
stellar members of Chamaeleon and to identify interlopers from the foreground
\epsilon Cha and \eta Cha associations. To this aim, we compile lists of
spectroscopically confirmed members of Chamaeleon I and II, \epsilon Cha and
\eta Cha, and of background objects in the same line of sight. Using Virtual
Observatory tools, we cross-match these lists with the UCAC3 catalogue to get
the proper motions of the objects. In the vector point diagram, we identify the
different moving groups, and use this information to study the membership of
proposed candidate members of the associations from the literature. For those
objects with available radial velocities, we compute their Galactic space
velocities. We look for correlations between the known properties of the
objects and their proper motions. The members of the dark clouds exhibit
clearly different proper motions from those of the foreground associations and
of the background stars. The data suggest that Chamaeleon II could have
different dynamical properties from Chamaeleon I. Although the two foreground
clusters \epsilon and \eta Chamaeleontis constitute two different proper motion
groups, they have similar spatial motions, which are different from the spatial
motion of Chamaeleon I. On the other hand, the space motions of the Chamaeleon
II stars look more similar to those of the foreground clusters than to the
Chamaeleon I stars, but the numbers are low. Hence, with the available data it
is unclear to what extent the stellar populations in both clouds are physically
connected to each other. We find no correlations between the proper motions and
the properties of the objects in either of the clouds
Infrared study of transitional disks in Ophiuchus with Herschel
Context. Observations of nearby star-forming regions with the Herschel Space
Observatory complement our view of the protoplanetary disks in Ophiuchus with
information about the outer disks. Aims. The main goal of this project is to
provide new far-infrared fluxes for the known disks in the core region of
Ophiuchus and to identify potential transitional disks using data from
Herschel. Methods. We obtained PACS and SPIRE photometry of previously
spectroscopically confirmed young stellar objects (YSO) in the region and
analysed their spectral energy distributions. Results. From an initial sample
of 261 objects with spectral types in Ophiuchus, we detect 49 disks in at least
one Herschel band. We provide new far-infrared fluxes for these objects. One of
them is clearly a new transitional disk candidate. Conclusions. The data from
Herschel Space Observatory provides fluxes that complement previous infrared
data and that we use to identify a new transitional disk candidate.Comment: 21 pages, with 5 figures. Accepted in Astronomy & Astrophysic
VISION - Vienna survey in Orion. III. Young stellar objects in Orion A
38 pages, 25 figures, Accepted for publication by A&A. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESOWe extend and refine the existing young stellar object (YSO) catalogs for the Orion A molecular cloud, the closest massive star-forming region to Earth. This updated catalog is driven by the large spatial coverage (18.3 deg^2, ~950 pc^2), seeing limited resolution (~0.7''), and sensitivity (Ks<19 mag) of the ESO-VISTA near-infrared survey of the Orion A cloud (VISION). Combined with archival mid- to far-infrared data, the VISTA data allow for a refined and more robust source selection. We estimate that among previously known protostars and pre-main-sequence stars with disks, source contamination levels (false positives) are at least âŒ7% and âŒ2.5%, respectively, mostly due to background galaxies and nebulosities. We identify 274 new YSO candidates using VISTA/Spitzer based selections within previously analyzed regions, and VISTA/WISE based selections to add sources in the surroundings, beyond previously analyzed regions. The WISE selection method recovers about 59% of the known YSOs in Orion A's low-mass star-forming part L1641, which shows what can be achieved by the all-sky WISE survey in combination with deep near-infrared data in regions without the influence of massive stars. The new catalog contains 2978 YSOs, which were classified based on the de-reddened mid-infrared spectral index into 188 protostars, 184 flat-spectrum sources, and 2606 pre-main-sequence stars with circumstellar disks. We find a statistically significant difference in the spatial distribution of the three evolutionary classes with respect to regions of high dust column-density, confirming that flat-spectrum sources are at a younger evolutionary phase compared to Class IIs, and are not a sub-sample seen at particular viewing angles.Peer reviewedFinal Accepted Versio
XMM-Newton observations of the nearby brown dwarf LP 944-20
The nearby (d=5.0 pc) brown dwarf LP944-20 was observed with the XMM-Newton
satellite on 07 January 2001. The target was detected with the Optical Monitor
(V=16.7360.081), but it was not detected during the ks
observation with the X-ray telescopes. We determine a upper limit for
the X-ray emission from this object of , equivalent to a luminosity ratio upper limit of . This measurement improves by a factor of 3 the previous
\emph{Chandra} limit on the quiescent X-ray flux. This is the most sensitive
limit ever obtained on the quiescent X-ray emission of a brown dwarf. Combining
the XMM data with previous \emph{ROSAT} and \emph{Chandra} data, we derive
flare duty cycles as a function of their luminosities. We find that very strong
flares [Log2.5] are very rare (less than 0.7% of the time).
Flares like the one detected by Chandra [Log4.1] have a duty
cycle of about 6%, which is lower than the radio flare duty cycle (13%).
When compared with other M dwarfs, LP944-20 appears to be rather inactive in
X-rays despite of its relative youth, fast rotation and its moderately strong
activity at radio wavelengths.Comment: 13 pages, 4 figures, accepted for publication in New Astronom
A spectral comparison of (379) Huenna and its satellite
We present near-infrared spectral measurements of Themis family asteroid
(379) Huenna (D~98 km) and its 6 km satellite using SpeX on the NASA IRTF. The
companion was farther than 1.5" from the primary at the time of observations
and was approximately 5 magnitudes dimmer. We describe a method for separating
and extracting the signal of a companion asteroid when the signal is not
entirely resolved from the primary. The spectrum of (379) Huenna has a broad,
shallow feature near 1 {\mu}m and a low slope, characteristic of C-type
asteroids. The secondary's spectrum is consistent with the taxonomic
classification of C-complex or X-complex. The quality of the data was not
sufficient to identify any subtle feature in the secondary's spectrum.Comment: 6 pages, 4 figures, 2 tables - Accepted for publication in Icaru