928 research outputs found
Herschel GASPS spectral observations of T Tauri stars in Taurus: unraveling far-infrared line emission from jets and discs
At early stages of stellar evolution young stars show powerful jets and/or
outflows that interact with protoplanetary discs and their surroundings.
Despite the scarce knowledge about the interaction of jets and/or outflows with
discs, spectroscopic studies based on Herschel and ISO data suggests that gas
shocked by jets and/or outflows can be traced by far-IR (FIR) emission in
certain sources. We want to provide a consistent catalogue of selected atomic
([OI] and [CII]) and molecular (CO, OH, and HO) line fluxes observed in
the FIR, separate and characterize the contribution from the jet and the disc
to the observed line emission, and place the observations in an evolutionary
picture. The atomic and molecular FIR (60-190 ) line emission of
protoplanetary discs around 76 T Tauri stars located in Taurus are analysed.
The observations were carried out within the Herschel key programme Gas in
Protoplanetary Systems (GASPS). The spectra were obtained with the
Photodetector Array Camera and Spectrometer (PACS). The sample is first divided
in outflow and non-outflow sources according to literature tabulations. With
the aid of archival stellar/disc and jet/outflow tracers and model predictions
(PDRs and shocks), correlations are explored to constrain the physical
mechanisms behind the observed line emission. The much higher detection rate of
emission lines in outflow sources and the compatibility of line ratios with
shock model predictions supports the idea of a dominant contribution from the
jet/outflow to the line emission, in particular at earlier stages of the
stellar evolution as the brightness of FIR lines depends in large part on the
specific evolutionary stage. [Abridged Abstract]Comment: 37 pages, 27 figures, accepted for publication in A&
Uncertainties in water chemistry in disks: An application to TW Hya
Context. This paper discusses the sensitivity of water lines to chemical
processes and radiative transfer for the protoplanetary disk around TW Hya. The
study focuses on the Herschel spectral range in the context of new line
detections with the PACS instrument from the Gas in Protoplanetary Systems
project (GASPS). Aims. The paper presents an overview of the chemistry in the
main water reservoirs in the disk around TW Hya. It discusses the limitations
in the interpretation of observed water line fluxes. Methods. ... (abbreviated)
Results. We report new line detections of p-H2O (3_22-2_11) at 89.99 micron and
CO J=18-17 at 144.78 micron for the disk around TW Hya. Disk modeling shows
that the far-IR fine structure lines ([OI], [CII]) and molecular submm lines
are very robust to uncertainties in the chemistry, while the water line fluxes
can change by factors of a few. The water lines are optically thick,
sub-thermally excited and can couple to the background continuum radiation
field. The low-excitation water lines are also sensitive to uncertainties in
the collision rates, e.g. with neutral hydrogen. The gas temperature plays an
important role for the [OI] fine structure line fluxes, the water line fluxes
originating from the inner disk as well as the high excitation CO, CH+ and OH
lines. Conclusions. Due to their sensitivity on chemical input data and
radiative transfer, water lines have to be used cautiously for understanding
details of the disk structure. Water lines covering a wide range of excitation
energies provide access to the various gas phase water reservoirs (inside and
outside the snow line) in protoplanetary disks and thus provide important
information on where gas-phase water is potentially located. Experimental
and/or theoretical collision rates for H2O with atomic hydrogen are needed to
diminish uncertainties from water line radiative transfer.Comment: accepted for publication in A&
Herschel evidence for disk flattening or gas depletion in transitional disks
Transitional disks are protoplanetary disks characterized by reduced near-
and mid-infrared emission with respect to full disks. This characteristic
spectral energy distribution indicates the presence of an optically thin inner
cavity within the dust disk believed to mark the disappearance of the
primordial massive disk. We present new Herschel Space Observatory PACS spectra
of [OI] 63 micron for 21 transitional disks. Our survey complements the larger
Herschel GASPS program "Gas in Protoplanetary Systems" (Dent et al. 2013) by
quadrupling the number of transitional disks observed with PACS at this
wavelength. [OI] 63 micron traces material in the outer regions of the disk,
beyond the inner cavity of most transitional disks. We find that transitional
disks have [OI] 63 micron line luminosities two times fainter than their full
disk counterparts. We self consistently determine various stellar properties
(e.g. bolometric luminosity, FUV excess, etc.) and disk properties (e.g. disk
dust mass, etc.) that could influence the [OI] 63 micron line luminosity and we
find no correlations that can explain the lower [OI] 63 micron line
luminosities in transitional disks. Using a grid of thermo-chemical
protoplanetary disk models, we conclude that either transitional disks are less
flared than full disks or they possess lower gas-to-dust ratios due to a
depletion of gas mass. This result suggests that transitional disks are more
evolved than their full disk counterparts, possibly even at large radii.Comment: Accepted for publication in ApJ; 52 pages, 16 figures, 8 table
Evolution of Young Brown Dwarf Disks in the Mid-Infrared
We have imaged two bona-fide brown dwarfs with TReCS/GEMINI-S and find
mid-infrared excess emission that can be explained by optically thick dust disk
models. In the case of the young (2Myr) Cha H1 we measure
fluxes at 10.4m and 12.3m that are fully consistent with a standard
flared disk model and prominent silicate emission. For the 10Myr old
brown dwarf 2MASS1207-3932 located in the TW Hydrae association we find excess
emission at 8.7m and 10.4m with respect to its photosphere, and
confirm disk accretion as likely cause of its strong activity. Disks around
brown dwarfs likely last at least as long as their low-mass stellar
counterparts in the T-Tauri phase. Grain growth, dust settling, and evolution
of the geometry of brown dwarfs disks may appear on a timescale of 10Myr and
can be witnessed by observations in the mid-infrared.Comment: 6 pages, 4 figure
Warm gas at 50 AU in the disk around Herbig Be star HD 100546
The disk atmosphere is one of the fundamental elements of theoretical models
of a protoplanetary disk. However, the direct observation of the warm gas (>>
100 K) at large radius of a disk (>> 10 AU) is challenging, because the line
emission from warm gas in a disk is usually dominated by the emission from an
inner disk. Our goal is to detect the warm gas in the disk atmosphere well
beyond 10 AU from a central star in a nearby disk system of the Herbig Be star
HD 100546. We measured the excitation temperature of the vibrational transition
of CO at incremental radii of the disk from the central star up to 50 AU, using
an adaptive optics system combined with the high-resolution infrared
spectrograph CRIRES at the VLT. The observation successfully resolved the line
emission with 0".1 angular resolution, which is 10 AU at the distance of HD
100546. Population diagrams were constructed at each location of the disk, and
compared with the models calculated taking into account the optical depth
effect in LTE condition. The excitation temperature of CO is 400-500 K or
higher at 50 AU away from the star, where the blackbody temperature in
equilibrium with the stellar radiation drops as low as 90 K. This is
unambiguous evidence of a warm disk atmosphere far away from the central star.Comment: 7 pages, 5 figures, A&A in pres
Childhood predictors and adult life success of adolescent delinquency abstainers
While much is known about adolescent delinquency, considerably less attention has been given to adolescent delinquency abstention. Understanding how or why some adolescents manage to abstain from delinquency during adolescence is informative for understanding and preventing adolescent (minor) delinquency. Using data from the Cambridge Study in Delinquent Development (N = 411 males) to compare abstainers, self-report delinquents and convicted delinquents we found five childhood factors (ages 8-10) that predicted adolescent abstention (ages 10-18). First, we find that adolescent abstainers possess characteristics opposite to those of convicted delinquents (namely, abstainers are high on honesty, conformity and family income). However, we also found that abstainers also share some childhood characteristics with convicted delinquents (namely, low popularity and low school achievement). A latent class analysis indicated that the mixed factors predicting abstention can be accounted for by two groups of abstainers: an adaptive group characterized by high honesty, and a maladaptive group characterized by low popularity and low school achievement. Further, validation of these two types of abstainers using data collected at age 48 suggested that adaptive abstainers outperform all other adolescents in general life success, whereas maladaptive abstainers only fare better than delinquent adolescents in terms of lower substance use and delinquency later in life
Herschel PACS Observations and Modeling of Debris Disks in the Tucana-Horologium Association
We present Herschel PACS photometry of seventeen B- to M-type stars in the 30
Myr-old Tucana-Horologium Association. This work is part of the Herschel Open
Time Key Programme "Gas in Protoplanetary Systems" (GASPS). Six of the
seventeen targets were found to have infrared excesses significantly greater
than the expected stellar IR fluxes, including a previously unknown disk around
HD30051. These six debris disks were fitted with single-temperature blackbody
models to estimate the temperatures and abundances of the dust in the systems.
For the five stars that show excess emission in the Herschel PACS photometry
and also have Spitzer IRS spectra, we fit the data with models of optically
thin debris disks with realistic grain properties in order to better estimate
the disk parameters. The model is determined by a set of six parameters:
surface density index, grain size distribution index, minimum and maximum grain
sizes, and the inner and outer radii of the disk. The best fitting parameters
give us constraints on the geometry of the dust in these systems, as well as
lower limits to the total dust masses. The HD105 disk was further constrained
by fitting marginally resolved PACS 70 micron imaging.Comment: 15 pages, 7 figures, Accepted to Ap
Exocomet signatures around the A-shell star Leo?
We present an intensive monitoring of high-resolution spectra of the Ca {\sc
ii} K line in the A7IV shell star Leo at very short (minutes, hours),
short (night to night), and medium (weeks, months) timescales. The spectra show
remarkable variable absorptions on timescales of hours, days, and months. The
characteristics of these sporadic events are very similar to most that are
observed toward the debris disk host star Pic, which are commonly
interpreted as signs of the evaporation of solid, comet-like bodies grazing or
falling onto the star. Therefore, our results suggest the presence of solid
bodies around Leo. To our knowledge, with the exception of Pic,
our monitoring has the best time resolution at the mentioned timescales for a
star with events attributed to exocomets. Assuming the cometary scenario and
considering the timescales of our monitoring, our results indicate that
Leo presents the richest environment with comet-like events known to date,
second only to Pic.Comment: A&A letters, proof-correcte
The structure of the protoplanetary disk surrounding three young intermediate mass stars. II. Spatially resolved dust and gas distribution
[Abridged] We present the first direct comparison of the distribution of the
gas, as traced by the [OI] 6300 AA emission, and the dust, as traced by the 10
micron emission, in the protoplanetary disk around three intermediate-mass
stars: HD 101412, HD 135344 B and HD 179218. N-band visibilities were obtained
with VLTI/MIDI. Simple geometrical models are used to compare the dust emission
to high-resolution optical spectra in the 6300 AA [OI] line of the same
targets. The disks around HD 101412 and HD 135344 B appear strongly flared in
the gas, but self-shadowed in the dust beyond ~ 2 AU. In both systems, the 10
micron emission is rather compact (< 2 AU) while the [OI] brightness profile
shows a double peaked structure. The inner peak is strongest and is consistent
with the location of the dust, the outer peak is fainter and is located at 5-10
AU. Spatially extended PAH emission is found in both disks. The disk around HD
179218 is flared in the dust. The 10 micron emission emerges from a double
ring-like structure with the first ring peaking at ~ 1 AU and the second at ~
20 AU. No dust emission is detected between ~ 3 -- 15 AU. The oxygen emission
seems also to come from a flared structure, however, the bulk of this emission
is produced between ~ 1 -- 10 AU. This could indicate a lack of gas in the
outer disk or could be due to chemical effects which reduce the abundance of OH
-- the parent molecule of the observed [OI] emission -- further away from the
star. The three systems, HD 179218, HD 135344 B and HD 101412, may form an
evolutionary sequence: the disk initially flared becomes flat under the
combined action of gas-dust decoupling, grain growth and dust settling.Comment: Accepted for publication in A&
DZ Cha: a bona fide photoevaporating disc
DZ Cha is a weak-lined T Tauri star (WTTS) surrounded by a bright
protoplanetary disc with evidence of inner disc clearing. Its narrow \Ha line
and infrared spectral energy distribution suggest that DZ Cha may be a
photoevaporating disc. We aim to analyse the DZ Cha star + disc system to
identify the mechanism driving the evolution of this object. We have analysed
three epochs of high resolution optical spectroscopy, photometry from the UV up
to the sub-mm regime, infrared spectroscopy, and J-band imaging polarimetry
observations of DZ Cha. Combining our analysis with previous studies we find no
signatures of accretion in the \Ha line profile in nine epochs covering a
time baseline of years. The optical spectra are dominated by
chromospheric emission lines, but they also show emission from the forbidden
lines [SII] 4068 and [OI] 6300 that indicate a disc outflow. The
polarized images reveal a dust depleted cavity of au in radius and two
spiral-like features, and we derive a disc dust mass limit of
M_\mathrm{dust}
80 \MJup) companions are detected down to 0\farcs07 ( au,
projected). The negligible accretion rate, small cavity, and forbidden line
emission strongly suggests that DZ Cha is currently at the initial stages of
disc clearing by photoevaporation. At this point the inner disc has drained and
the inner wall of the truncated outer disc is directly exposed to the stellar
radiation. We argue that other mechanisms like planet formation or binarity
cannot explain the observed properties of DZ Cha. The scarcity of objects like
this one is in line with the dispersal timescale ( yr) predicted
by this theory. DZ Cha is therefore an ideal target to study the initial stages
of photoevaporation.Comment: A&A in press, language corrections include
- …