787 research outputs found
The young cluster NGC 2282 : a multi-wavelength perspective
We present the analysis of the stellar content of NGC~2282, a young cluster
in the Monoceros constellation, using deep optical and IPHAS photometry
along with infrared (IR) data from UKIDSS and -IRAC. Based on the
stellar surface density analysis using nearest neighborhood method, the radius
of the cluster is estimated as 3.15\arcmin. From optical spectroscopic
analysis of 8 bright sources, we have classified three early B-type members in
the cluster, which includes, HD 289120, a previously known B2V type star, a
Herbig Ae/Be star (B0.5 Ve) and a B5 V star. From spectrophotometric analyses,
the distance to the cluster has been estimated as 1.65 kpc. The -band
extinction map is estimated using nearest neighborhood technique, and the mean
extinction within the cluster area is found to be A 3.9 mag. Using
IR colour-colour criteria and H-emission properties, we have
identified a total of 152 candidate young stellar objects (YSOs) in the region,
of which, 75 are classified as Class II, 9 are Class I YSOs. Our YSO catalog
also includes 50 H-emission line sources, identified using slitless
spectroscopy and IPHAS photometry data. Based on the optical and near-IR
colour-magnitude diagram analyses, the cluster age has been estimated to be in
the range of 2 5 Myr, which is in agreement with the estimated age from
disc fraction ( 58\%). Masses of these YSOs are found to be
0.12.0 M. Spatial distribution of the candidate YSOs shows spherical
morphology, more or less similar to the surface density map.Comment: 16 pages, 19 Figure
Exploring Foundations of Time-Independent Density Functional Theory for Excited-States
Based on the work of Gorling and that of Levy and Nagy, density-functional
formalism for many Fermionic excited-states is explored through a careful and
rigorous analysis of the excited-state density to external potential mapping.
It is shown that the knowledge of the ground-state density is a must to fix the
mapping from an excited-state density to the external potential. This is the
excited-state counterpart of the Hohenberg-Kohn theorem, where instead of the
ground-state density the density of the excited-state gives the true many-body
wavefunctions of the system. Further, the excited-state Kohn-Sham system is
defined by comparing it's non-interacting kinetic energy with the true kinetic
energy. The theory is demonstrated by studying a large number of atomic
systems.Comment: submitted to J. Chem. Phy
W40 region in the Gould Belt : An embedded cluster and H II region at the junction of filaments
We present a multiwavelength study of W40 star-forming region using IR
observations in UKIRT JHK bands, Spitzer IRAC bands & Herschel PACS bands; 2.12
micron H2 narrow-band imaging; & radio observations from GMRT (610 & 1280 MHz),
in a FoV of ~34'x40'. Spitzer observations along with NIR observations are used
to identify 1162 Class II/III & 40 Class I sources in the FoV. The NN stellar
surface density analysis shows that majority of these YSOs constitute the
embedded cluster centered on the source IRS1A South. Some YSOs, predominantly
younger population, are distributed along & trace the filamentary structures at
lower stellar surface density. The cluster radius is obtained as 0.44pc -
matching well with the extent of radio emission - with a peak density of
650pc^-2. The JHK data is used to map the extinction which is subsequently used
to compute the cloud mass. It has resulted in 126 Msun & 71 Msun for the
central cluster & the northern IRS5 region, respectively. H2 narrow-band
imaging displays significant emission, which prominently resembles fluorescent
emission arising at the borders of dense regions. Radio analysis shows this
region as having blister morphology, with the radio peak coinciding with a
protostellar source. Free-free emission SED analysis is used to obtain physical
parameters of the overall region & the IRS5 sub-region. This multiwavelength
scenario is suggestive of star formation having resulted from merging of
multiple filaments to form a hub. Star formation seems to have taken place in
two successive epochs, with the first epoch traced by the central cluster & the
high-mass star(s) - followed by a second epoch which is spreading into the
filaments as uncovered by the Class I sources & even younger protostellar
sources along the filaments. The IRS5 HII region displays indications of
swept-up material which has possibly led to the formation of protostars.Comment: 17 pages, 12 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Deep GeMS/GSAOI near-infrared observations of N159W in the Large Magellanic Cloud
Aims. The formation and properties of star clusters at the edge of H II
regions are poorly known, partly due to limitations in angular resolution and
sensitivity, which become particularly critical when dealing with extragalactic
clusters. In this paper we study the stellar content and star-formation
processes in the young N159W region in the Large Magellanic Cloud.
Methods. We investigate the star-forming sites in N159W at unprecedented
spatial resolution using JHKs-band images obtained with the GeMS/GSAOI
instrument on the Gemini South telescope. The typical angular resolution of the
images is of 100 mas, with a limiting magnitude in H of 22 mag (90 percent
completeness). Photometry from our images is used to identify candidate young
stellar objects (YSOs) in N159W. We also determine the H-band luminosity
function of the star cluster at the centre of the H II region and use this to
estimate its initial mass function (IMF).
Results. We estimate an age of 2 + or - 1 Myr for the central cluster, with
its IMF described by a power-law with an index of gamma = - 1.05 + or - 0.2 ,
and with a total estimated mass of 1300 solar mass. We also identify 104
candidate YSOs, which are concentrated in clumps and subclusters of stars,
principally at the edges of the H II region. These clusters display signs of
recent and active star-formation such as ultra-compact H II regions, and
molecular outflows. This suggests that the YSOs are typically younger than the
central cluster, pointing to sequential star-formation in N159W, which has
probably been influenced by interactions with the expanding H II bubble
Study of the filamentary infrared dark cloud G192.76+00.10 in the S254-S258 OB complex
We present results of a high resolution study of the filamentary infrared
dark cloud G192.76+00.10 in the S254-S258 OB complex in several molecular
species tracing different physical conditions. These include three
isotopologues of carbon monoxide (CO), ammonia (NH), carbon monosulfide
(CS). The aim of this work is to study the general structure and kinematics of
the filamentary cloud, its fragmentation and physical parameters. The gas
temperature is derived from the NH and
CO(2--1) lines and the CO(1--0), CO(2--1) emission is used
to investigate the overall gas distribution and kinematics. Several dense
clumps are identified from the CS(2--1) data. Values of the gas temperature lie
in the ranges K, column density reaches the value 5.1
10 cm. The width of the filament is of order 1 pc. The masses of
the dense clumps range from M to M.
They appear to be gravitationally unstable. The molecular emission shows a gas
dynamical coherence along the filament. The velocity pattern may indicate
longitudinal collapse.Comment: 10 pages, 9 figures, accepted for publication in Research in
Astronomy and Astrophysic
Low-mass young stellar population and star formation history of the cluster IC 1805 in the W4 H{\sc ii} region
W4 is a giant H{\sc ii} region ionized by the OB stars of the cluster
IC~1805. The H{\sc ii} region/cluster complex has been a subject of numerous
investigations as it is an excellent laboratory for studying the feedback
effect of massive stars on the surrounding region. However, the low-mass
stellar content of the cluster IC~1805 remains poorly studied till now. With
the aim to unravel the low-mass stellar population of the cluster, we present
the results of a multiwavelength study based on deep optical data obtained with
the Canada-France-Hawaii Telescope, infrared data from 2MASS, Space
Telescope and X-ray data from Space Telescope. The present optical
dataset is complete enough to detect stars down to 0.2~M, which is the
deepest optical observations so far for the cluster. We identified 384
candidate young stellar objects (YSOs; 101 Class I/II and 283 Class III) within
the cluster using various colour-colour and colour-magnitude diagrams. We
inferred the mean age of the identified YSOs to be 2.5 Myr and mass in
the range 0.3 - 2.5 M. The mass function of our YSO sample has a power
law index of -1.23 0.23, close to the Salpeter value (-1.35), and
consistent with those of other star-forming complexes. We explored the disk
evolution of the cluster members and found that the diskless sources are
relatively older compared to the disk bearing YSO candidates. We examined the
effect of high-mass stars on the circumstellar disks and found that within
uncertainties, the influence of massive stars on the disk fraction seems to be
insignificant. We also studied the spatial correlation of the YSOs with the
distribution of gas and dust of the complex to conclude that IC 1805 would have
formed in a large filamentary cloud.Comment: Accepted for publication in MNRAS; 34 pages, 10 figure
Star formation activity in the Galactic H II region Sh2-297
We present a multiwavelength study of the Galactic H II region Sh2-297,
located in Canis Major OB1 complex. Optical spectroscopic observations are used
to constrain the spectral type of ionizing star HD 53623 as B0V. The classical
nature of this H II region is affirmed by the low values of electron density
and emission measure, which are calculated to be 756 cm^-3 and 9.15 x 10^5
cm^-6 pc using the radio continuum observations at 610 and 1280 MHz, and VLA
archival data at 1420 MHz. To understand local star formation, we identified
the young stellar object (YSO) candidates in a region of area ~ 7.5' x 7.5'
centered on Sh2-297 using grism slitless spectroscopy (to identify the Halpha
emission line stars), and near infrared (NIR) observations. NIR YSO candidates
are further classified into various evolutionary stages using color-color (CC)
and color-magnitude (CM) diagrams, giving 50 red sources (H-K > 0.6) and 26
Class II-like sources. The mass and age range of the YSOs are estimated to be ~
0.1 - 2 Msolar and 0.5 - 2 Myr using optical (V/V-I) and NIR (J/J-H) CM
diagrams. The mean age of the YSOs is found to be ~ 1 Myr, which is of the
order of dynamical age of 1.07 Myr of the H II region. Using the estimated
range of visual extinction (1.1 - 25 mag) from literature and NIR data for the
region, spectral energy distribution (SED) models have been implemented for
selected YSOs which show masses and ages to be consistent with estimated
values. The spatial distribution of YSOs shows an evolutionary sequence,
suggesting triggered star formation in the region. The star formation seems to
have propagated from the ionizing star towards the cold dark cloud LDN1657A
located west of Sh2-297.Comment: 19 pages, 13 figures, 3 tables. Accepted for publication in The
Astrophysical Journa
Young Stellar Population of the Bright-Rimmed Clouds BRC 5, BRC 7 and BRC 39
Bright-rimmed clouds (BRCs), illuminated and shaped by nearby OB stars, are
potential sites of recent/ongoing star formation. Here we present an optical
and infrared photometric study of three BRCs: BRC 5, BRC 7 and BRC 39 to obtain
a census of the young stellar population, thereby inferring the star formation
scenario, in these regions. In each BRC, the Class I sources are found to be
located mostly near the bright rim or inside the cloud, whereas the Class II
sources are preferentially outside, with younger sources closer to the rim.
This provides strong support to sequential star formation triggered by
radiation driven implosion due to the UV radiation. Moreover, each BRC contains
a small group of young stars being revealed at its head, as the next-generation
stars. In particular, the young stars at the heads of BRC 5 and BRC 7 are found
to be intermediate/high mass stars, which, under proper conditions, may
themselves trigger further star birth, thereby propagating star formation out
to long distances.Comment: 30 pages, 7 Figures, 6 Tables, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
The molecular complex associated with the Galactic HII region Sh2-90: a possible site of triggered star formation
We investigate the star formation activity in the molecular complex
associated with the Galactic HII region Sh2-90, using radio-continuum maps
obtained at 1280 MHz and 610 MHz, Herschel Hi-GAL observations at 70 -- 500
microns, and deep near-infrared observation at JHK bands, along with Spitzer
observations. Sh2-90 presents a bubble morphology in the mid-IR (size ~ 0.9 pc
x 1.6 pc). Radio observations suggest it is an evolved HII region with an
electron density ~ 144 cm^-3, emission measure ~ 6.7 x 10^4 cm^-6 pc and a
ionized mass ~ 55 Msun. From Hi-GAL observations it is found that the HII
region is part of an elongated extended molecular cloud (size ~ 5.6 pc x 9.7
pc, H_2 column density >= 3 x 10^21 cm^-2 and dust temperature 18 -- 27 K) of
total mass >= 1 x 10^4 Msun. We identify the ionizing cluster of Sh2-90, the
main exciting star being an O8--O9 V star. Five cold dust clumps (mass ~ 8 --
95 Msun), four mid-IR blobs around B stars, and a compact HII region are found
at the edge of the bubble.The velocity information derived from CO (J=3-2) data
cubes suggests that most of them are associated with the Sh2-90 region. 129
YSOs are identified (Class I, Class II, and near-IR excess sources). The
majority of the YSOs are low mass (<= 3 Msun) sources and they are distributed
mostly in the regions of high column density. Four candidate Class 0/I MYSOs
have been found; they will possibly evolve to stars of mass >= 15 Msun. We
suggest multi-generation star formation is present in the complex. From the
evidences of interaction, the time scales involved and the evolutionary status
of stellar/protostellar sources, we argue that the star formation at the
immediate border/edges of Sh2-90 might have been triggered by the expanding HII
region. However, several young sources in this complex are probably formed by
some other processes.Comment: 22 pages, 22 figures, accepted for publication in Astronomy and
Astrophysic
Pre-main-sequence population in NGC 1893 region: X-ray properties
Continuing the attempt to understand the properties of the stellar content in
the young cluster NGC 1893 we have carried out a comprehensive multi-wavelength
study of the region. The present study focuses on the X-ray properties of
T-Tauri Stars (TTSs) in the NGC 1893 region. We found a correlation between the
X-ray luminosity, , and the stellar mass (in the range 0.22.0 \msun) of
TTSs in the NGC 1893 region, similar to those reported in some other young
clusters, however the value of the power-law slope obtained in the present
study ( 0.9) for NGC 1893 is smaller than those (1.4 - 3.6)
reported in the case of TMC, ONC, IC 348 and Chameleon star forming regions.
However, the slope in the case of Class III sources (Weak line TTSs) is found
to be comparable to that reported in the case of NGC 6611 ( 1.1). It is
found that the presence of circumstellar disks has no influence on the X-ray
emission. The X-ray luminosity for both CTTSs and WTTSs is found to decrease
systematically with age (in the range 0.4 Myr - 5 Myr). The decrease of
the X-ray luminosity of TTSs (slope -0.6) in the case of NGC 1893 seems
to be faster than observed in the case of other star-forming regions (slope
-0.2 to -0.5). There is indication that the sources having relatively large NIR
excess have relatively lower values. TTSs in NGC 1893 do not follow the
well established X-ray activity - rotation relation as in the case of
main-sequence stars.Comment: 10 pages, 7 figures, Accepted for publication in New Astronom
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