21 research outputs found
Searching for reflected light from Bootis b with high-resolution ground-based spectroscopy: Approaching the contrast barrier
It is challenging to measure the starlight reflected from exoplanets because
of the extreme contrast with their host stars. For hot Jupiters, this contrast
is in the range of to , depending on their albedo, radius
and orbital distance. Searches for reflected light have been performed since
the first hot Jupiters were discovered, but with very limited success because
hot Jupiters tend to have low albedo values due to the general absence of
reflective cloud decks. The aim of this study is to search for reflected light
from Boo b, a hot Jupiter with one of the brightest host stars. Since
its discovery in 1997, it has been the subject of several reflected-light
searches using high-dispersion spectroscopy. Here we aim to combine these data
in to a single meta-analysis. We analysed more than 2,000 archival
high-dispersion spectra obtained with the UVES, ESPaDOnS, NARVAL UES and
HARPS-N spectrographs during various epochs between 1998 and 2013. Each
spectrum was first cleaned of the stellar spectrum and subsequently
cross-correlated with a PHOENIX model spectrum. These were then Doppler shifted
to the planet rest-frame and co-added in time, weighted according to the
expected signal-to-noise of the planet signal. We reach a 3 upper limit
of the planet to star contrast of . Assuming a planet
radius of 1.15 , this corresponds to an optical albedo of 0.12 between
400-700 nm. This low albedo is in line with secondary eclipse and phase curve
observations of other hot Jupiters using space-based observatories, as well as
theoretical predictions of their reflective properties.Comment: 15 pages, 13 figures, accepted for publication in Astronomy and
Astrophysic
Survey of Orion Disks with ALMA (SODA) II: UV-driven disk mass loss in L1641 and L1647
External FUV irradiation of protoplanetary disks has an important impact on
their evolution and ability to form planets. However, nearby (<300 pc)
star-forming regions lack sufficiently massive young stars, while the Trapezium
Cluster and NGC 2024 have complicated star-formation histories and their O-type
stars' intense radiation fields () destroy disks too quickly to
study this process in detail. We study disk mass loss driven by intermediate
(10 - 1000 ) FUV radiation fields in L1641 and L1647, where it is driven
by more common A0 and B-type stars. Using the large (N=873) sample size offered
by the Survey of Orion Disks with ALMA (SODA), we search for trends in the
median disk dust mass with FUV field strength across the region as a whole and
in two separate regions containing a large number of irradiated disks. For
radiation fields between 1 - 100 , the median disk mass in the most
irradiated disks drops by a factor over the lifetime of the region,
while the 95th percentile of disk masses drops by a factor 4 over this range.
This effect is present in multiple populations of stars, and localized in
space, to within 2 pc of ionizing stars. We fit an empirical irradiation - disk
mass relation for the first time: . This work demonstrates
that even intermediate FUV radiation fields have a significant impact on the
evolution of protoplanetary disks.Comment: Accepted to A&A Letters. 5 pages, 4 figure
Demographics of disks around young very low-mass stars and brown dwarfs in Lupus
Funding: This work was partly supported by the Italian Ministero dell Istruzione, Università e Ricerca through the grant Progetti Premiali 2012 – iALMA (CUP C52I13000140001), by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Ref no. FOR2634/1TE1024/1-1, and by the DFG cluster of excellence Origins (www.origins-cluster.de), and by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 823823 (RISE DUSTBUSTERS project). T.H. acknowledges support from the European Research Council under the Horizon 2020 Framework Program via the ERC Advanced Grant Origins 83 24 28. KM acknowledges funding by the Science and Technology Foundation of Portugal (FCT), grants No. IF/00194/2015 and PTDC/FISAST/28731/2017. CM, SF, AM acknowledge an ESO Fellowship. M.T. has been supported by the UK Science and Technology research Council (STFC).We present new 890 μm continuum ALMA observations of five brown dwarfs (BDs) with infrared excess in Lupus I and III, which in combination with four previously observed BDs allowed us to study the millimeter properties of the full known BD disk population of onestar-forming region. Emission is detected in five out of the nine BD disks. Dust disk mass, brightness profiles, and characteristic sizes ofthe BD population are inferred from continuum flux and modeling of the observations. Only one source is marginally resolved, allowing for the determination of its disk characteristic size. We conduct a demographic comparison between the properties of disks around BDs and stars in Lupus. Due to the small sample size, we cannot confirm or disprove a drop in the disk mass over stellar mass ratio for BDs, as suggested for Ophiuchus. Nevertheless, we find that all detected BD disks have an estimated dust mass between 0.2 and 3.2 M⊙; these results suggest that the measured solid masses in BD disks cannot explain the observed exoplanet population, analogous to earlier findings on disks around more massive stars. Combined with the low estimated accretion rates, and assuming that the mm-continuum emission is a reliable proxy for the total disk mass, we derive ratios of Ṁacc/Mdisk that are significantly lower than in disks around more massive stars. If confirmed with more accurate measurements of disk gas masses, this result could imply a qualitatively different relationship between disk masses and inward gas transport in BD disks.Publisher PDFPeer reviewe
Measuring the ratio of the gas and dust emission radii of protoplanetary disks in the Lupus star-forming region
We perform a comprehensive demographic study of the CO extent relative to
dust of the disk population in the Lupus clouds, in order to find indications
of dust evolution and possible correlations with other properties. We increase
up to 42 the number of disks of the region with measured CO and dust sizes
(, ) from observations with the Atacama
Large Millimeter/submillimeter Array (ALMA). The sizes are obtained from
modeling the CO line emission and continuum emission at
mm with an empirical function (Nuker profile or Gaussian function).
The CO emission is more extended than the dust continuum, with a
/ median value of 2.5, for
the entire population and for a sub-sample with high completeness. 6 disks,
around of the Lupus disk population have a size ratio above 4. Based on
thermo-chemical modeling, this value can only be explained if the disk has
undergone grain growth and radial drift. These disks do not have unusual
properties in terms of stellar mass (), disk mass
(), CO and dust sizes (,
), and mass accretion. We search for correlations between
the size ratio and , , and
: only a weak monotonic anti-correlation with the
is found. The lack of strong correlations is remarkable and
suggests that the bulk of the population may be in a similar evolutionary
stage, independent of the stellar and disk properties. These results should be
further investigated, since the optical depth difference between CO and dust
continuum may play a role in the inferred size ratios. Lastly, the CO emission
for the majority of the disks is consistent with optically thick emission and
an average CO temperature of around 30 K.Comment: Accepted for publication on A&A, 14 pages of main text with 5
figures, and 11 pages of appendices A, B, C, D, E and F with 13 figure
XUE. Molecular inventory in the inner region of an extremely irradiated Protoplanetary Disk
We present the first results of the eXtreme UV Environments (XUE) James Webb
Space Telescope (JWST) program, that focuses on the characterization of planet
forming disks in massive star forming regions. These regions are likely
representative of the environment in which most planetary systems formed.
Understanding the impact of environment on planet formation is critical in
order to gain insights into the diversity of the observed exoplanet
populations. XUE targets 15 disks in three areas of NGC 6357, which hosts
numerous massive OB stars, among which some of the most massive stars in our
Galaxy. Thanks to JWST we can, for the first time, study the effect of external
irradiation on the inner ( au), terrestrial-planet forming regions of
proto-planetary disks. In this study, we report on the detection of abundant
water, CO, CO, HCN and CH in the inner few au of XUE 1, a highly
irradiated disk in NGC 6357. In addition, small, partially crystalline silicate
dust is present at the disk surface. The derived column densities, the
oxygen-dominated gas-phase chemistry, and the presence of silicate dust are
surprisingly similar to those found in inner disks located in nearby,
relatively isolated low-mass star-forming regions. Our findings imply that the
inner regions of highly irradiated disks can retain similar physical and
chemical conditions as disks in low-mass star-forming regions, thus broadening
the range of environments with similar conditions for inner disk rocky planet
formation to the most extreme star-forming regions in our Galaxy.Comment: Accepted for publication in ApJ Letters. 20 pages, 7 figure
Survey of Orion Disks with ALMA (SODA)
Context. External far-ultraviolet (FUV) irradiation of protoplanetary disks has an important impact on their evolution and ability to form planets. However, nearby ( 104 G0) destroy disks too quickly to study this process in detail.
Aims. We study disk mass loss driven by intermediate (10 − 1000 G0) FUV radiation fields in L1641 and L1647, where it is driven by more common A0- and B-type stars.
Methods. Using the large (N = 873) sample size offered by the Survey of Orion Disks with ALMA (SODA), we searched for trends in the median disk dust mass with FUV field strength across the region as a whole and in two separate regions containing a large number of irradiated disks.
Results. For radiation fields between 1 − 100 G0, the median disk mass in the most irradiated disks drops by a factor ∼2 over the lifetime of the region, while the 95th percentile of disk masses drops by a factor 4 over this range. This effect is present in multiple populations of stars, and localized in space, to within 2 pc of ionizing stars. We fitted an empirical irradiation – disk mass relation for the first time: .
Conclusions. This work demonstrates that even intermediate FUV radiation fields have a significant impact on the evolution of protoplanetary disks
Survey of Orion Disks with ALMA (SODA) - I. Cloud-level demographics of 873 protoplanetary disks
(Abridged) Surveys of protoplanetary disks in nearby star-forming regions
(SFRs) have provided important information on their demographics, but due to
their sample sizes, they cannot be used to study how disk properties vary with
the environment. We conduct a survey of the unresolved millimeter continuum
emission of 873 protoplanetary disks identified by Spitzer in the L1641 and
L1647 regions of the Orion A cloud. This is the largest such survey yet,
allowing us to identify even weak trends in the median disk mass as a function
of position in the cloud and cluster membership. The sample detection rates and
median masses are also compared to those of nearby (<300 pc) SFRs. The sample
was observed with ALMA at 225 GHz, with a median rms of 0.08 mJy/beam (1.5
M). The data were reduced and imaged using an innovative parallel
data processing approach. We detect 58% (502/873) of the observed disks. This
includes 20 disks with dust masses >100 M, and two objects
associated with extended dust emission. We infer a median disk dust mass in the
full sample of M. In L1641 and L1647 median dust
masses are M and
M, respectively. The disk mass distribution of the full sample is
similar to that of nearby low-mass SFRs at similar ages of 1-3 Myr. We find
only weak trends in disk (dust) masses with galactic longitude and between the
YSO clusters identified in the sample, with median masses varying by
50%. Age differences may explain these median disk mass variations. Apart from
this, disk masses are essentially constant at scales of ~100 pc. This also
suggests that the majority of disks, even in different SFRs, are formed with
similar initial masses and evolve at similar rates, assuming no external
irradiation, with disk mass loss rates of M/yr.Comment: Accepted in A&A. 19 pages, 13 figures, 5 tables in the main text; 5
pages, 1 table and 5 additional figures in appendice
Bright C<sub>2</sub>H emission in protoplanetary discs in Lupus: high volatile C/O > 1 ratios
Context. Recent ALMA surveys in different star-forming regions have shown that CO emission in protoplanetary discs is much fainter than expected. Accordingly, CO-based gas masses and gas to dust ratios are orders of magnitude lower than previously thought. This may be explained either as fast gas dispersal, or as chemical evolution and locking up of volatiles in larger bodies leading to the low observed CO fluxes. The latter processes lead to enhanced C/O ratios in the gas, which may be reflected in enhanced abundances of carbon-bearing molecules like C2H. Aims. The goal of this work is to use C2H observations to understand whether low CO fluxes are caused by volatile depletion or by fast gas dissipation. Methods. We present ALMA Cycle 4 C2H (N = 3–2, J = 7∕2–5∕2, F = 4–3 and F = 3–2) observations of a subsample of nine sources in the Lupus star-forming region. The integrated C2H emission is determined and compared to previous CO isotopologue observations and physical-chemical model predictions. Results. Seven out of nine discs are detected in C2H, whose line emission is almost as bright as 13CO. All detections are significantly brighter than the typical sensitivity of the observations, hinting at a bimodal distribution of the C2H line intensities. This conclusion is strengthened when our observations are compared with additional C2H observations of other discs. When compared with physical-chemical models, the observed C2H fluxes can be reproduced only if some level of volatile carbon and oxygen depletion is allowed and [C]/[O] > 1 in the gas. Models with reduced gas-to-dust ratios near unity however fail to reproduce the observed C2H line luminosity. A steeper than linear correlation between C2H and CN emission line is found for the Lupus discs. This is linked to the fact that C2H emission lines are affected more strongly by [C]/[O] variations than CN lines. Ring-like structures are detected both in C2H and in continuum emission but, as for CN, they do not seem to be connected. The source Sz 71 shows ring-shaped emission in both C2H and CN with the location of the peak intensity coinciding, within our 30 au resolution. Conclusions. Our new ALMA C2H observations favour volatile carbon and oxygen depletion rather than fast gas dispersal to explain the faint CO observations for most of the discs. This result has implications for disc-evolution and planet-formation theories, as disc gas masses may be larger than expected if CO is considered to be the main carbon carrier in the gas phase
An ALMA Survey of lambda Orionis Disks: From Supernovae to Planet Formation
Protoplanetary disk surveys by the Atacama Large Millimeter/submillimeter Array (ALMA) are now probing a range of environmental conditions, from low-mass star-forming regions like Lupus to massive OB clusters like σ Orionis. Here we conduct an ALMA survey of protoplanetary disks in λ Orionis, an ~5 Myr old OB cluster in Orion with dust mass sensitivities comparable to the surveys of nearby regions (~0.4 M ⊕). We assess how massive OB stars impact planet formation, in particular from the supernova that may have occurred ~1 Myr ago in the core of λ Orionis; studying these effects is important, as most planetary systems, including our solar system, are likely born in cluster environments. We find that the effects of massive stars, in the form of presupernova feedback and/or a supernova itself, do not appear to significantly reduce the available planet-forming material otherwise expected at this evolved age. We also compare a lingering massive "outlier" disk in λ Orionis to similar systems in other evolved regions, hypothesizing that these outliers host companions in their inner disks that suppress disk dispersal to extend the lifetimes of their outer primordial disks. We conclude with numerous avenues for future work that highlight how λ Orionis still has much to teach us about perhaps one of the most common types of planet-forming environments in the Galaxy