634 research outputs found
Near infrared imaging of the cometary globule CG12
Cometary globule 12 is a relatively little investigated medium- and low mass
star forming region 210 pc above the Galactic plane. NIR J, H, and Ks imaging
and stellar photometry is used to analyse the stellar content and the structure
of CG 12. Several new members and member candidates of the CG 12 stellar
cluster were found. The new members include in particular a highly embedded
source with a circumstellar disk or shell and a variable star with a
circumstellar disk which forms a binary with a previously known A spectral type
cluster member. The central source of the known collimated molecular outflow in
CG 12 and an associated "hourglass"-shaped object due to reflected light from
the source were also detected. HIRES-enhanced IRAS images are used together
with SOFI J,H,Ks imaging to study the two associated IRAS point sources,
13546-3941 and 13547-3944. Two new 12 micrometer sources coinciding with NIR
excess stars were detected in the direction of IRAS 13546-3941. The IRAS
13547-3944 emission at 12 and 25 micrometers originates in the Herbig AeBe star
h4636n and the 60 and 100 micrometer emission from an adjacent cold source.Comment: Accepted Astronomy and Astrophysics Oct. 15 200
Extending the limits of globule detection -- ISOPHOT Serendipity Survey Observations of interstellar clouds
A faint MJysr bipolar globule was discovered with the
ISOPHOT 170 m Serendipity Survey (ISOSS). ISOSS J 20246+6541 is a cold
( K) FIR source without an IRAS pointsource counterpart.
In the Digitized Sky Survey B band it is seen as a 3\arcmin size bipolar
nebulosity with an average excess surface brightness of
mag/\arcsec . The CO column density distribution determined by
multi-isotopic, multi-level CO measurements with the IRAM-30m telescope agrees
well with the optical appearance. An average hydrogen column density of
cm was derived from both the FIR and CO data. Using a
kinematic distance estimate of 400 pc the NLTE modelling of the CO, HCO,
and CS measurements gives a peak density of cm. The
multiwavelength data characterise ISOSS 20246+6541 as a representative of a
class of globules which has not been discovered so far due to their small
angular size and low 100m brightness. A significant overabundance of
CO is found . This is likely due to
isotope selective chemical processes.Comment: 5 pages, 3 figure
Probing the structure of a birthplace of intermediate-mass stars: Ammonia cores in Lynds 1340
Lynds 1340, a molecular cloud forming intermediate-mass stars, has been
mapped in the NH_3(1,1) and (2,2) transitions with the Effelsberg 100m
telescope. We observed the whole area of the cloud where C18O emission was
detected earlier, at a 40 arcsec grid, with additional positions towards the
C18O peaks and optically invisible IRAS point sources. Our observations covered
an area of 170 arcmin^2, corresponding to about 5.15 pc^2 at a distance of 600
pc, and revealed 10 ammonia cores. The cores, occupying some 7% of the mapped
area, probably represent the highest density regions of L1340. Their total mass
is 80 solar mass, about 6% of the mass traced by C18O. Six cores are associated
with optically invisible IRAS point sources. Their average nonthermal line
width is 0.78 kms^{-1}, while the same quantity for the four starless cores is
0.28 kms^{-1}. We suggest that the narrow-line cores are destined to form
low-mass stars, whereas small groups of intermediate-mass stars are being
formed in the turbulent cores. The features traced by NH_3, 13CO, C18O and HI
obey the line width-size relation log Delta v_{NT} = 0.41(0.06)log R_{1/2}+
0.12(0.06). Comparison of sizes, densities and nonthermal line widths of
ammonia cores with those of C18O and 13CO structures supports the scenario in
which core formation has been induced by turbulent fragmentation. The typical
physical properties of the ammonia cores of L1340, R_{1/2} =0.08 pc,
T_{kin}=13.8 K, Delta v_{total}=0.64 kms^{-1}, and M =9 solar mass are close to
those of the high-mass star forming Perseus and Orion B clouds.Comment: 13 pages, 11 figures. Accepted by A&
A Pan-Carina YSO Catalog: Intermediate-Mass Young Stellar Objects in the Carina Nebula Identified Via Mid-Infrared Excess Emission
We present a catalog of 1439 young stellar objects (YSOs) spanning the 1.42
deg^2 field surveyed by the Chandra Carina Complex Project (CCCP), which
includes the major ionizing clusters and the most active sites of ongoing star
formation within the Great Nebula in Carina. Candidate YSOs were identified via
infrared (IR) excess emission from dusty circumstellar disks and envelopes,
using data from the Spitzer Space Telescope Vela--Carina survey and the
Two-Micron All Sky Survey. We model the 1--24 /mu m IR spectral energy
distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO
Catalog (PCYC) is dominated by intermediate-mass (2 Msun < m < 10 Msun) objects
with disks, including Herbig Ae/Be stars and their less evolved progenitors.
The PCYC provides a valuable complementary dataset to the CCCP X-ray source
catalogs, identifying 1029 YSOs in Carina with no X-ray detection. We also
catalog 410 YSOs with X-ray counterparts, including 62 candidate protostars.
Candidate protostars with X-ray detections tend to be more evolved than those
without. In most cases, X-ray emission apparently originating from
intermediate-mass, disk-dominated YSOs is consistent with the presence of
low-mass companions, but we also find that X-ray emission correlates with
cooler stellar photospheres and higher disk masses. We suggest that
intermediate-mass YSOs produce X-rays during their early pre-main sequence
evolution, perhaps driven by magnetic dynamo activity during the convective
atmosphere phase, but this emission dies off as the stars approach the main
sequence. Extrapolating over the stellar initial mass function scaled to the
PCYC population, we predict a total population of >2x10^4 YSOs and a
present-day star formation rate (SFR) of >0.008 Msun/yr. The global SFR in the
Carina Nebula, averaged over the past ~5 Myr, has been approximately constant.Comment: 23 pages, 11 figures, accepted for the ApJS Special Issue on the
Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011.
All 16 CCCP Special Issue papers, including a version of this article with
high-quality figures and full electronic tables, are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html (through 2011
at least
High-Mass Cloud Cores in the eta Carinae Giant Molecular Cloud
We carried out an unbiased survey for massive dense cores in the giant
molecular cloud associated with eta Carinae with the NANTEN telescope in 12CO,
13CO, and C18O 1-0 emission lines. We identified 15 C18O cores. Two of the 15
cores are associated with IRAS point sources whose luminosities are larger than
10^4 Lo, which indicates that massive star formation is occuring within these
cores. Five cores including the two with IRAS sources are associated with MSX
point sources. We detected H13CO+ (1-0) emission toward 4 C18O cores, one of
which is associated with neither IRAS nor MSX point sources. This core shows
the presence of a bipolar molecular outflow in 12CO (2-1), which indicates that
star formation is also occuring in the core. In total, six C18O cores out of 15
are experienced star formation, and at least 2 of 15 are massive-star forming
cores in the eta Car GMC. We found that massive star formation occurs
preferentially in cores with larger column density, mass, number density, and
smaller ratio of virial mass to LTE mass Mvir/M. We also found that the cores
in the eta Car GMC are characterized by large line width and Mvir/M on average
compared to the cores in other GMCs. We investigated the origin of a large
amount of turbulence in the eta Car GMC. We propose the possibility that the
large turbulence was pre-existing when the GMC was formed, and is now
dissipating. Mechanisms such as multiple supernova explosions in the Carina
flare supershell may have contributed to form a GMC with a large amount of
turbulence.Comment: 41 pages, including 11 fugures and 9 tables. Accepted by ApJ. Author
changed. Paper with high resolution figures is available at
http://astrol.cias.osakafu-u.ac.jp/~yonekura/work/paper/etaCar
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
The Spitzer c2d Survey of Nearby Dense Cores: VI. The Protostars of Lynds Dark Nebula 1221
Observations of Lynds Dark Nebula 1221 from the Spitzer Space Telescope are
presented. These data show three candidate protostars towards L1221, only two
of which were previously known. The infrared observations also show signatures
of outflowing material, an interpretation which is also supported by radio
observations with the Very Large Array. In addition, molecular line maps from
the Five College Radio Astronomy Observatory are shown.
One-dimensional dust continuum modelling of two of these protostars, IRS1 and
IRS3, is described. These models show two distinctly different protostars
forming in very similar environments. IRS1 shows a higher luminosity and larger
inner radius of the envelope than IRS3. The disparity could be caused by a
difference in age or mass, orientation of outflow cavities, or the impact of a
binary in the IRS1 core.Comment: accepted for publication in Ap
The structure of the cometary globule CG 12: a high latitude star forming region
The structure of the high galactic latitude Cometary Globule 12 (CG 12) has
been investigated by means of radio molecular line observations. Detailed, high
signal to noise ratio maps in C18O (1-0), C18O (2-1) and molecules tracing high
density gas, CS (3-2), DCO+ (2-1) and H13CO+ (1-0), are presented. The C18O
line emission is distributed in a 10' long North-South elongated lane with two
strong maxima, CG12 N(orth) and CG12 S(outh). In CG12 S the high density
tracers delineate a compact core, DCO+ core, which is offset by 15" from the
C18O maximum. The observed strong C18O emission traces the surface of the DCO+
core or a separate, adjacent cloud component. The emission in high density
tracers is weak in CG12 N and especially the H13CO+, DCO+ and N2H+ lines are
+0.5 km/s offset in velocity with respect to the C18O lines. Evidence is
presented that the molecular gas is highly depleted. The observed strong C18O
emission towards CG12 N originates in the envelope of this depleted cloud
component or in a separate entity seen in the same line of sight. The C18O
lines in CG 12 were analyzed using Positive Matrix Factorization, PMF. The
shape and the spatial distribution of the individual PMF factors fitted
separately to the C18O (1-0) and (2-1) transitions were consistent with each
other. The results indicate a complex velocity and line excitation structure in
the cloud. Besides separate cloud velocity components the C18O line shapes and
intensities are influenced by excitation temperature variations caused by e.g,
the molecular outflow or by molecular depletion. Assuming a distance of 630 pc
the size of the CG 12 compact head, 1.1 pc by 1.8 pc, and the C18O mass larger
than 100 Msun are comparable to those of other nearby low/intermediate mass
star formation regions.Comment: 18 pages, 17 figures Accepted A&A Sep. 22 200
Multifractal Scaling, Geometrical Diversity, and Hierarchical Structure in the Cool Interstellar Medium
Multifractal scaling (MFS) refers to structures that can be described as a
collection of interwoven fractal subsets which exhibit power-law spatial
scaling behavior with a range of scaling exponents (concentration, or
singularity, strengths) and dimensions. The existence of MFS implies an
underlying multiplicative (or hierarchical, or cascade) process. Panoramic
column density images of several nearby star- forming cloud complexes,
constructed from IRAS data and justified in an appendix, are shown to exhibit
such multifractal scaling, which we interpret as indirect but quantitative
evidence for nested hierarchical structure. The relation between the dimensions
of the subsets and their concentration strengths (the "multifractal spectrum'')
appears to satisfactorily order the observed regions in terms of the mixture of
geometries present: strong point-like concentrations, line- like filaments or
fronts, and space-filling diffuse structures. This multifractal spectrum is a
global property of the regions studied, and does not rely on any operational
definition of "clouds.'' The range of forms of the multifractal spectrum among
the regions studied implies that the column density structures do not form a
universality class, in contrast to indications for velocity and passive scalar
fields in incompressible turbulence, providing another indication that the
physics of highly compressible interstellar gas dynamics differs fundamentally
from incompressible turbulence. (Abstract truncated)Comment: 27 pages, (LaTeX), 13 figures, 1 table, submitted to Astrophysical
Journa
Candidate X-ray-Emitting OB Stars in the Carina Nebula Identified Via Infrared Spectral Energy Distributions
We report the results of a new survey of massive, OB stars throughout the
Carina Nebula using the X-ray point source catalog provided by the Chandra
Carina Complex Project (CCCP) in conjunction with infrared (IR) photometry from
the Two Micron All-Sky Survey and the Spitzer Space Telescope Vela--Carina
survey. Mid-IR photometry is relatively unaffected by extinction, hence it
provides strong constraints on the luminosities of OB stars, assuming that
their association with the Carina Nebula, and hence their distance, is
confirmed. We fit model stellar atmospheres to the optical (UBV) and IR
spectral energy distributions (SEDs) of 182 OB stars with known spectral types
and measure the bolometric luminosity and extinction for each star. We find
that the extinction law measured toward the OB stars has two components:
Av=1--1.5 mag produced by foreground dust with a ratio of total-to-selective
absorption Rv=3.1 plus a contribution from local dust with Rv>4.0 in the Carina
molecular clouds that increases as Av increases. Using X-ray emission as a
strong indicator of association with Carina, we identify 94 candidate OB stars
with Lbol\geq10^4 Lsun by fitting their IR SEDs. If the candidate OB stars are
eventually confirmed by follow-up spectroscopic observations, the number of
cataloged OB stars in the Carina Nebula will increase by ~50%. Correcting for
incompleteness due to OB stars falling below the Lbol cutoff or the CCCP
detection limit, these results potentially double the size of the young massive
stellar population.Comment: 19 pages, 8 figures, accepted for the ApJS Special Issue on the
Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011.
All 16 CCCP Special Issue papers, including a version of this article with
high-quality figures, are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html (through 2011
at least
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