34 research outputs found
New infrared star clusters in the Northern and Equatorial Milky Way with 2MASS
We carried out a survey of infrared star clusters and stellar groups on the
2MASS J, H and K_s all-sky release Atlas in the Northern and Equatorial Milky
Way (350 < l < 360, 0 < l < 230). The search in this zone complements that in
the Southern Milky Way (Dutra et al. 2003a). The method concentrates efforts on
the directions of known optical and radio nebulae. The present study provides
167 new infrared clusters, stellar groups and candidates. Combining the two
studies for the whole Milky Way, 346 infrared clusters, stellar groups and
candidates were discovered, whereas 315 objects were previously known. They
constitute an important new sample for future detailed studies.Comment: Accepted to Astronomy and Astrophysic
GM 2-4 - a signpost for low and intermediate mass star formation
We present a multi-wavelength study of the region towards the GM 2-4 nebula
and the nearby source IRAS 05373+2340. Our near-infrared H2 1-0 S(1) line
observations reveal various shock-excited features which are part of several
bipolar outflows. We identify candidates for the driving sources of the
outflows from a comparison of the multi-waveband archival data-sets and SED
modelling. The SED spectral slope (\alpha(IRAC)) for all the protostars in the
field was then compared with the visual extinction map. This comparison
suggests that star formation is progressing from NE to SW across this region
The IC2118 association: new T Tauri stars in high-latitude molecular clouds
We identified new pre-main sequence stars in the region of high-latitude
molecular clouds associated with the reflection nebula IC2118, around l = 208
degr and b = -27 degr. The stars were selected as T Tauri candidates in
objective prism plates obtained with the Schmidt telescope of Konkoly
Observatory. Results of spectroscopic follow-up observations, carried out with
the FLAIR spectrograph installed on the UK Schmidt and with ALFOSC on Nordic
Optical Telescope, are presented in this paper. Based on spectral types,
presence of emission lines and lithium absorption line, we identified five
classical T Tauri stars and a candidate weak-line T Tauri star projected on the
molecular clouds, as well as two candidate pre-main sequence stars outside the
nebulous region. Using the near infrared magnitudes obtained from the 2MASS All
Sky Catalog. we determined the masses and ages of these stars. We found that
the five classical T Tauri stars projected on the clouds are physically related
to them, whereas the other stars are probably background objects. Adopting a
distance of 210 pc for IC2118 (Kun et al. 2001) and using Palla & Stahler's
(1999) evolutionary tracks we derived an average age of 2.5 million yrs and a
mass interval of 0.4--1.0 M_sun for the members of the IC2118 association.Comment: 11 pages, 6 figures, accepted for publication by Astronomy and
Astrophysic
Inner disc rearrangement revealed by dramatic brightness variations in the young star PV Cep
Young Sun-like stars at the beginning of the pre-main sequence (PMS)
evolution are surrounded by accretion discs and remnant protostellar envelopes.
Photometric and spectroscopic variations of these stars are driven by
interactions of the star with the disc. Time scales and wavelength dependence
of the variability carry information on the physical mechanisms behind these
interactions. We conducted multi-epoch, multi-wavelength study of PV Cep, a
strongly variable, accreting PMS star. By combining our own observations from
2004-2010 with archival and literature data, we show that PV Cep started a
spectacular fading in 2005, reaching an I_C-band amplitude of 4 mag. Analysis
of variation of the optical and infrared fluxes, colour indices, and emission
line fluxes suggests that the photometric decline in 2005-2009 resulted from an
interplay between variable accretion and circumstellar extinction: since the
central luminosity of the system is dominated by accretion, a modest drop in
the accretion rate could induce the drastic restructuring of the inner disc.
Dust condensation in the inner disc region might have resulted in the
enhancement of the circumstellar extinction.Comment: 11 pages, 4 figures, accepted for publication by MNRAS. 3 online
tables adde
The young stellar population in the Serpens Cloud Core: An ISOCAM survey
We present results from an ISOCAM survey in the two broad band filters LW2
(5-8.5 mu) and LW3 (12-18 mu) of a 0.13 square degree coverage of the Serpens
Main Cloud Core. A total of 392 sources were detected in the 6.7 mu band and
139 in the 14.3 mu band to a limiting sensitivity of ~ 2 mJy. Only about 50% of
the mid-IR excess sources show excesses in the near-IR J-H/H-K diagram. In the
central Cloud Core the Class I/Class II number ratio is 19/18, i.e. about 10
times larger than in other young embedded clusters such as rho Ophiuchi or
Chamaeleon. The mid-IR fluxes of the Class I and flat-spectrum sources are
found to be on the average larger than those of Class II sources. Stellar
luminosities are estimated for the Class II sample, and its luminosity function
is compatible with a coeval population of about 2 Myr which follows a three
segment power-law IMF. For this age about 20% of the Class IIs are found to be
young brown dwarf candidates. The YSOs are in general strongly clustered, the
Class I sources more than the Class II sources, and there is an indication of
sub-clustering. The sub-clustering of the protostar candidates has a spatial
scale of 0.12 pc. These sub-clusters are found along the NW-SE oriented ridge
and in very good agreement with the location of dense cores traced by
millimeter data. The smallest clustering scale for the Class II sources is
about 0.25 pc, similar to what was found for rho Ophiuchi. Our data show
evidence that star formation in Serpens has proceeded in several phases, and
that a ``microburst'' of star formation has taken place very recently, probably
within the last 10^5 yrs.Comment: 25 pages, 14 figures, accepted by A&A March 18th, see also
http://www.not.iac.es/~amanda
A near IR imaging survey of intermediate and high-mass young stellar outflow candidates
We have carried out a near-infrared imaging survey of luminous young stellar
outflow candidates using the United Kingdom Infrared Telescope. Observations
were obtained in the broad band K (2.2 mu) and through narrow band filters at
the wavelengths of H_2 v=1--0 S(1) (2.1218 mu) and Br gamma (2.166 mu) lines.
Fifty regions were imaged with a field of view of 2.2 X 2.2 arcmin^2. Several
young embedded clusters are unveiled in our near-infrared images. 76% of the
objects exhibit H_2 emission and 50% or more of the objects exhibit aligned H_2
emission features suggesting collimated outflows, many of which are new
detections. These observations suggest that disk accretion is probably the
leading mechanism in the formation of stars, at least up to late O spectral
types. The young stellar objects responsible for many of these outflows are
positively identified in our images based on their locations with respect to
the outflow lobes, 2MASS colours and association with MSX, IRAS, millimetre and
radio sources. The close association of molecular outflows detected in CO with
the H_2 emission features produced by shock excitation by jets from the young
stellar objects suggests that the outflows from these objects are jet-driven.
Towards strong radio emitting sources, H_2 jets were either not detected or
were weak when detected, implying that most of the accretion happens in the
pre-UCHII phase; accretion and outflows are probably weak when the YSO has
advanced to its UCHII stage.Comment: 64 pages, 53 figures, Accepted for publication in the MNRA
A Single Distance Sample of Molecular Outflows from High-Mass Young Stellar Objects
We have made 12CO 2-1 and 1-0 maps of eleven molecular outflows associated
with intermediate to high-mass young stellar objects (YSOs) in order to
establish whether the correlations between outflow parameters and source
bolometric luminosity hold in the high-mass regime. It is important to consider
the effects of Malmquist-type biases when looking at high-mass YSOs, as they
are generally much more distant than their low mass counterparts. We therefore
chose only objects located at ~2kpc. We find that the relations show much more
scatter than is seen in similar studies of low-mass YSOs. We also find that the
mass-spectrum is significantly steeper in high-mass outflows, indicating a
larger mass-fraction at lower velocities, a low collimation factor (~1-2) and
no Hubble-like relationship.Comment: Accepted for publication in A&A, 14 pages, including 13 figure
Dense gas and the nature of the outflows
We present the results of the observations of the (J,K)=(1,1) and the
(J,K)=(2,2) inversion transitions of the NH3 molecule toward a large sample of
40 regions with molecular or optical outflows, using the 37 m radio telescope
of the Haystack Observatory. We detected NH3 emission in 27 of the observed
regions, which we mapped in 25 of them. Additionally, we searched for the
6{16}-5{23} H2O maser line toward six regions, detecting H2O maser emission in
two of them, HH265 and AFGL 5173. We estimate the physical parameters of the
regions mapped in NH3 and analyze for each particular region the distribution
of high density gas and its relationship with the presence of young stellar
objects. From the global analysis of our data we find that in general the
highest values of the line width are obtained for the regions with the highest
values of mass and kinetic temperature. We also found a correlation between the
nonthermal line width and the bolometric luminosity of the sources, and between
the mass of the core and the bolometric luminosity. We confirm with a larger
sample of regions the conclusion of Anglada et al. (1997) that the NH3 line
emission is more intense toward molecular outflow sources than toward sources
with optical outflow, suggesting a possible evolutionary scheme in which young
stellar objects associated with molecular outflows progressively lose their
neighboring high-density gas, weakening both the NH3 emission and the molecular
outflow in the process, and making optical jets more easily detectable as the
total amount of gas decreases.Comment: 27 pages, 37 figures. Accepted for publication in Astronomy and
Astrophysics. Abstract is abridge
Astrophysics in 2005
We bring you, as usual, the Sun and Moon and stars, plus some galaxies and a new section on astrobiology. Some highlights are short (the newly identified class of gamma-ray bursts, and the Deep Impact on Comet 9P/ Tempel 1), some long (the age of the universe, which will be found to have the Earth at its center), and a few metonymic, for instance the term "down-sizing" to describe the evolution of star formation rates with redshift