72 research outputs found
Accretion signatures in the X-shooter spectrum of the substellar companion to SR12
About a dozen substellar companions orbiting young stellar objects or pre-main sequence stars at several hundred au have been identified in the last decade. These objects are interesting both due to the uncertainties surrounding their formation, and because their large separation from the host star offers the potential to study the atmospheres of young giant planets and brown dwarfs. Here, we present X-shooter spectroscopy of SR 12 C, a ∼2 Myr young brown dwarf orbiting SR 12 at an orbital separation of 1083 au. We determine the spectral type, gravity, and effective temperature via comparison with models and observational templates of young brown dwarfs. In addition, we detect and characterize accretion using several accretion tracers. We find SR 12 C to be a brown dwarf of spectral type L0 ± 1, log g = 4 ± 0.5, an effective temperature of 2600 ± 100 K. Our spectra provide clear evidence for accretion at a rate of ∼10−10 M⊙ yr−1. This makes SR 12 one of the few sub-stellar companions with a reliable estimate for its accretion rate. A comparison of the ages and accretion rates of sub-stellar companions with young isolated brown dwarfs does not reveal any significant differences. If further accretion rate measurements of a large number of substellar companions can confirm this trend, this would hint towards a similar formation mechanism for substellar companions at large separations and isolated brown dwarfs
Bipolar molecular outflow of the very low-mass star Par-Lup3-4
Very low-mass stars are known to have jets and outflows, which is indicative
of a scaled-down version of low-mass star formation. However, only very few
outflows in very low-mass sources are well characterized. We characterize the
bipolar molecular outflow of the very low-mass star Par-Lup3-4, a 0.12
M object known to power an optical jet. We observed Par-Lup3-4 with
ALMA in Bands 6 and 7, detecting both the continuum and CO molecular gas. In
particular, we studied three main emission lines: CO(2-1), CO(3-2), and
CO(3-2). Our observations reveal for the first time the base of a
bipolar molecular outflow in a very low-mass star, as well as a stream of
material moving perpendicular to the primary outflow of this source. The
primary outflow morphology is consistent with the previously determined jet
orientation and disk inclination. The outflow mass is
, with an outflow rate of
A new fitting to the
spectral energy distribution suggests that Par-Lup3-4 may be a binary system.
We have characterized Par-Lup3-4 in detail, and its properties are consistent
with those reported in other very low-mass sources. This source provides
further evidence that very low-mass sources form as a scaled-down version of
low-mass stars.Comment: 20 pages, 11 figures, 5 tables. Accepted in A&
Discovery of a Fast Expanding Shell in the Inside-out Born-Again Planetary Nebula HuBi 1 Through High-Dispersion Integral Field Spectroscopy
HuBi 1 has been proposed to be member of the rare class of born-again
planetary nebulae (PNe), i.e., its central star experienced a very late thermal
pulse and ejected highly-processed material at high speeds inside the old
hydrogen-rich PN. In this letter we present GTC MEGARA integral field
spectroscopic observations of the innermost regions of HuBi 1 at high spectral
resolution km s and multi-epoch sub-arcsec images obtained
yr apart. The analysis of these data indicates that the inner
regions of HuBi 1 were ejected yr ago and expand at velocities
km s, in excellent agreement with the born-again scenario.
The unprecedented tomographic capabilities of the GTC MEGARA high-dispersion
observations used here reveal that the ejecta in HuBi 1 has a shell-like
structure, in contrast to the disrupted disk and jet morphology of the ejecta
in other born-again PNe.Comment: 7 pages, 5 Figures; accepted to ApJ
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
White dwarfs with planetary remnants in the era of Gaia - I. Six emission line systems
White dwarfs with emission lines from gaseous debris discs are among the rarest examples of planetary remnant hosts, but at the same time they are key objects for studying the final evolutionary stage of planetary systems. Making use of the large number of white dwarfs identified in Gaia Data Release 2 (DR2), we are conducting a survey of planetary remnants and here we present the first results of our search: six white dwarfs with gaseous debris discs. This first publication focuses on the main observational properties of these objects and highlights their most unique features. Three systems in particular stand out: WD J084602.47+570328.64 displays an exceptionally strong infrared excess that defies the standard model of a geometrically thin, optically thick dusty debris disc; WD J213350.72+242805.93 is the hottest gaseous debris disc host known with \mbox{T_{\mathrm{eff}}}=29\,282 K; and WD J052914.32-340108.11 in which we identify a record number of 51 emission lines from five elements. These discoveries shed light on the underlying diversity in gaseous debris disc systems and bring the total number of these objects to 21. With these numbers we can now start looking at the properties of these systems as a class of objects rather than on a case-by-case basis
Implementation of the Random Forest Method for the Imaging Atmospheric Cherenkov Telescope MAGIC
The paper describes an application of the tree classification method Random
Forest (RF), as used in the analysis of data from the ground-based gamma
telescope MAGIC. In such telescopes, cosmic gamma-rays are observed and have to
be discriminated against a dominating background of hadronic cosmic-ray
particles. We describe the application of RF for this gamma/hadron separation.
The RF method often shows superior performance in comparison with traditional
semi-empirical techniques. Critical issues of the method and its implementation
are discussed. An application of the RF method for estimation of a continuous
parameter from related variables, rather than discrete classes, is also
discussed.Comment: 16 pages, 8 figure
Unfolding of differential energy spectra in the MAGIC experiment
The paper describes the different methods, used in the MAGIC experiment, to
unfold experimental energy distributions of cosmic ray particles (gamma-rays).
Questions and problems related to the unfolding are discussed. Various
procedures are proposed which can help to make the unfolding robust and
reliable. The different methods and procedures are implemented in the MAGIC
software and are used in most of the analyses.Comment: Submitted to NIM
Discovery of Very High Energy gamma-rays from 1ES 1011+496 at z=0.212
We report on the discovery of Very High Energy (VHE) gamma-ray emission from
the BL Lacertae object 1ES1011+496. The observation was triggered by an optical
outburst in March 2007 and the source was observed with the MAGIC telescope
from March to May 2007. Observing for 18.7 hr we find an excess of 6.2 sigma
with an integrated flux above 200 GeV of (1.58 photons
cm s. The VHE gamma-ray flux is >40% higher than in March-April
2006 (reported elsewhere), indicating that the VHE emission state may be
related to the optical emission state. We have also determined the redshift of
1ES1011+496 based on an optical spectrum that reveals the absorption lines of
the host galaxy. The redshift of z=0.212 makes 1ES1011+496 the most distant
source observed to emit VHE gamma-rays up to date.Comment: 4 pages, 6 figures, minor changes to fit the ApJ versio
Discovery of Very High Energy -Rays from Markarian~180 Triggered by an Optical Outburst
The high-frequency-peaked BL Lacertae object Markarian~180 (Mrk~180) was
observed to have an optical outburst in 2006 March, triggering a Target of
Opportunity observation with the MAGIC telescope. The source was observed for
12.4 hr and very high energy -ray emission was detected with a
significance of 5.5 . An integral flux above 200 GeV of
was measured, corresponding to
11% of the Crab Nebula flux. A rather soft spectrum with a photon index of
has been determined. No significant flux variation was found.Comment: Accepted by ApJ Letters, minor revision
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