94 research outputs found
A Keplerian gaseous disk around the B0 star R Mon
We present high-angular resolution observations of the circumstellar disk
around the massive Herbig Be star R Mon (M~8 Msun) in the continuum at 2.7mm
and 1.3mm and the CO 1->0 and 2->1 rotational lines. Based on the new 1.3mm
continuum image we estimate a disk mass (gas+dust) of 0.007 Msun and an outer
radius of <150 AU. Our CO images are consistent with the existence of a
Keplerian rotating gaseous disk around this star. Up to our knowledge, this is
the most clear evidence for the existence of Keplerian disks around massive
stars reported thus far. The mass and physical characteristics of this disk are
similar to thoseof the more evolved T Tauri stars and indicate a shorter
timescale for the evolution and dispersal of circumstellar disks around massive
stars which lose most of their mass before the star becomes visible.Comment: 5 page
The dusty disk around VV Ser
We have carried out observations at millimeter and centimeter wavelengths
towards VV Ser using the Plateau de Bure Interferometer and the Very Large
Array. This allows us to compute the SED from near infrared to centimeter
wavelengths. The modeling of the full SED has provided insight into the dust
properties and a more accurate value of the disk mass.
The mass of dust in the disk around VV Ser is found to be about 4 10^(-5)
Msun, i.e. 400 times larger than previous estimates. Moreoever, the SED can
only be accounted for assuming dust stratification in the vertical direction
across the disk. The existence of small grains (0.25--1 micron) in the disk
surface is required to explain the emission at near- and mid-infrared
wavelengths. The fluxes measured at millimeter wavelengths imply that the dust
grains in the midplane have grown up to very large sizes, at least to some
centimeters.Comment: To appear in Ap
Massive young disks around Herbig Ae stars
Herbig Ae stars (HAe) are the precursors of Vega-type systems and, therefore,
crucial objects in planet formation studies. Thus far, only a few disks
associated with HAe stars have been studied using millimetre interferometers.
Our aim is to determine the dust evolution and the lifetime of the disks
associated with Herbig Ae stars. We imaged the continuum emission at 3 mm and
1.3 mm of the Herbig Ae/Be stars BD+61154, RR Tau, VY Mon and LkHa 198 using
the Plateau de Bure Interferometer (PdBI). These stars are in the upper end of
the stellar mass range of the Herbig Ae stars (stellar mass greater than 3
solar masses). Our measurements were used to complete the Spectral Energy
Distribution (SED). The modelling of the SED, in particular the FIR-mm part,
allow us to determine the masses and dust properties of these disks. We
detected the disks associated with BD+61154, RR Tau and VY Mon with disk masses
of 0.35 Msun, 0.05 Msun and 0.40 Msun respectively. The disk around LkHa 198
was not detected with an upper limit to the disk mass of 0.004 Msun. We
detected, however, the disks associated with the younger stellar objects LkHa
198--IR and LkHa 198-mm that are located in the vicinity of LkHa 198. The
fitting of the mm part of the SED reveal that the grains in the mid-plane of
the disks around BD+61154, RR Tau and VY Mon have sizes of 1--1000 microns.
Therefore, grains have not grown to centimetre sizes in these disks yet. These
massive (M>3 Msun) and young (about 1 Myr) HAe stars are surrounded by massive
(>0.04 Msun) disks with grains of micron-millimetre sizes. Although grain
growth is proceeding in these disks, their evolutionary stage is prior to the
formation of planetesimals. These disks are less evolved than those detected
around T Tauri and Herbig Be stars
Dissecting an intermediate-mass (IM) protostar: Chemical differentiation in IC1396N
We have carried out high-angular resolution (1.4") observations in the
continuum at 3.1mm and in the N2H+ 1-0, CH3CN 5_k-4_k and 13CS 2-1 lines using
the Plateau de Bure Interferometer (PdBI) towards the intermediate mass (IM)
protostar IRAS21391+5802 (IC1396N). In addition, we have merged the PdBI images
with previous BIMA (continuum data at 1.2mm and 3.1mm) and single-dish (N2H+
1-0) data to have a comprehensive description of the region. The combination of
our data with BIMA and 30m data show that the bipolar outflow associated has
completely eroded the initial molecular globule. The 1.2mm and 3.1mm continuum
emissions are extended along the outflow axis tracing the warm walls of the
biconical cavity. Most of the molecular gas, however, is located in an
elongated feature in the direction perpendicular to the outflow. A strong
chemical differentiation is detected across the molecular toroid, with the N2H+
1-0 emission absent in the inner region.This chemical differentiation can be
understood in terms of the different gas kinetic temperature. The
[CH3CN]/[N2H+] ratio increases by 5 orders of magnitude with gas temperature,
for temperatures between 20K and 100K. The CH3CN abundance towards IRAM 2A, the
most massive protostellar core, is similar to that found in hot corinos and
lower than that expected towards IM and high mass hot cores. This could
indicate that IRAM 2A is a low mass or at most Herbig Ae star (IRAM 2A) instead
of the precursor of a massive Be star. Alternatively, the low CH3CN abundance
could also be the consequence of IRAM 2A being a Class 0/I transition object
which has already formed a small photodissociation region (PDR).Comment: accepted A&
Protostellar clusters in intermediate-mass (IM) star forming regions
The transition between the low density groups of T Tauri stars and the high
density clusters around massive stars occurs in the intermediate-mass (IM)
range (M2--8 M). High spatial resolution studies of IM young
stellar objects (YSO) can provide important clues to understand the clustering
in massive star forming regions.
Aims: Our aim is to search for clustering in IM Class 0 protostars. The high
spatial resolution and sensitivity provided by the new A configuration of the
Plateau de Bure Interferometer (PdBI) allow us to study the clustering in these
nearby objects.
Methods: We have imaged three IM Class 0 protostars (Serpens-FIRS 1, IC 1396
N, CB 3) in the continuum at 3.3 and 1.3mm using the PdBI. The sources have
been selected with different luminosity to investigate the dependence of the
clustering process on the luminosity of the source.
Results: Only one millimeter (mm) source is detected towards the low
luminosity source Serpens--FIRS 1. Towards CB 3 and IC1396 N, we detect two
compact sources separated by 0.05 pc. The 1.3mm image of IC 1396 N, which
provides the highest spatial resolution, reveal that one of these cores is
splitted in, at least, three individual sources.Comment: 4 pages, 3 figures, accepted for publication in Astronomy and
Astrophysics Letters (Special Feature IRAM/PdB
The abundance of C18O and HDO in the envelope and hot core of the intermediate mass protostar NGC 7129 FIRS 2
NGC 7129 FIRS 2 is a young intermediate-mass (IM) protostar, which is
associated with two energetic bipolar outflows and displays clear signs of the
presence of a hot core. It has been extensively observed with ground based
telescopes and within the WISH Guaranteed Time Herschel Key Program. We present
new observations of the C18O 3-2 and the HDO 3_{12}-2_{21} lines towards NGC
7129 FIRS 2. Combining these observations with Herschel data and modeling their
emissions, we constrain the C18O and HDO abundance profiles across the
protostellar envelope. In particular, we derive the abundance of C18O and HDO
in the hot core. The intensities of the C18O lines are well reproduced assuming
that the C18O abundance decreases through the protostellar envelope from the
outer edge towards the centre until the point where the gas and dust reach the
CO evaporation temperature (~20-25 K) where the C18O is released back to the
gas phase. Once the C18O is released to the gas phase, the modelled C18O
abundance is found to be ~1.6x10^{-8}, which is a factor of 10 lower than the
reference abundance. This result is supported by the non-detection of C18O 9-8,
which proves that even in the hot core (T_k>100 K) the CO abundance must be 10
times lower than the reference value. Several scenarios are discussed to
explain this C18O deficiency. One possible explanation is that during the
pre-stellar and protostellar phase, the CO is removed from the grain mantles by
reactions to form more complex molecules. Our HDO modeling shows that the
emission of HDO 3_{12}-2_{21} line is maser and comes from the hot core
(T_k>100 K). Assuming the physical structure derived by Crimier et al. (2010),
we determine a HDO abundance of ~0.4 - 1x10^{-7} in the hot core of this IM
protostar, similar to that found in the hot corinos NGC 1333 IRAS 2A and IRAS
16293-2422.Comment: 10 pages, 7 figure
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