95 research outputs found
Multi-epoch infrared photometry of the star forming region G173.58+2.45
We present a multi-epoch infrared photometric study of the intermediate-mass
star forming region G173.58+2.45. Photometric observations are obtained using
the near-infrared filters and narrow-band filters centered at the
wavelengths of H (1-0) S(1) (2.122 m) and [FeII] (1.644 m) lines.
The H image shows molecular emission from shocked gas, implying the
presence of multiple star formation and associated outflow activity. We see
evidence for several collimated outflows. The most extended jet is at least
0.25 pc in length and has a collimation factor of 10, which may be
associated with a binary system within the central cluster, resolved for the
first time here. This outflow is found to be episodic; probably occurring or
getting enhanced during the periastron passage of the binary. We also find that
the variable star in the vicinity of the outflow source, which was known as a
FU Ori type star, is probably not a FU Ori object. However, it does drive a
spectacular outflow and the variability is likely to be related to accretion,
when large clouds of gas and dust spiral in towards the central source. Many
other convincing accretion-outflow systems and YSO candidates are discovered in
the field.Comment: 15 pages, 9 figures, accepted for publication in MNRA
Near-Infrared and Optical Studies of the fast nova V4643 Sgr (Nova Sagittarii 2001)
V4643 Sagittarii or Nova Sagittarii 2001 was discovered in outburst at 7.7
mag. on 2001 February 24. Here, we present near-infrared results of this fast
classical nova obtained in the early decline phase in 2001 March followed by
optical observations about one month later. Subsequently we also present
near-infrared spectra taken later in the nova's evolution, about four months
after the outburst, when V4643 Sgr had entered the coronal phase. The spectra
in the early decline phase are dominated by emission lines of the HI Brackett
series and also the Paschen beta and gamma lines. We study the cause of the
excitation of the the OI line at 1.128 micron and discuss the variation in its
strength with time after outburst. We discuss the role of optical depth effects
on the observed strengths of the hydrogen Brackett and Paschen lines and
discuss possible reasons for the puzzling behavior of the Br gamma line
strength and whether it is correlated with the OI 1.128 micron line behavior.
An optical spectrum is presented which shows that HeII lines are the most
prominent features - after HI - to be seen in early 2001 April. We present and
also discuss spectra taken in 2001 June and August which prominently show
coronal lines of [Si VI] and [Si VII] at 1.9641 micron and 2.4807 micron
respectively.Comment: Accepted in MNRA
Optical/IR studies of Be stars in NGC 6834 with emphasis on two specific stars
We present optical and infrared photometric and spectroscopic studies of two
Be stars in the 70--80-Myr-old open cluster NGC 6834. NGC 6834(1) has been
reported as a binary from speckle interferometric studies whereas NGC 6834(2)
may possibly be a gamma Cas-like variable. Infrared photometry and spectroscopy
from the United Kingdom Infrared Telescope (UKIRT), and optical data from
various facilities are combined with archival data to understand the nature of
these candidates. High signal-to-noise near-IR spectra obtained from UKIRT have
enabled us to study the optical depth effects in the hydrogen emission lines of
these stars. We have explored the spectral classification scheme based on the
intensity of emission lines in the and bands and contrasted it with the
conventional classification based on the intensity of hydrogen and helium
absorption lines. This work also presents hitherto unavailable UBV CCD
photometry of NGC 6834, from which the evolutionary state of the Be stars is
identified.Comment: Published in Research in Astronomy and Astrophysics, RAA 14 (2014)
1173-1192, 20 pages, 10 figure
A parsec-scale outflow from the luminous YSO IRAS 17527-2439
Imaging observations of IRAS 17527-2439 are obtained in the near-IR JHK
photometric bands and in a narrow-band filter centred at the wavelength of the
H_2 1-0 S(1) line. The continuum-subtracted H_2 image is used to identify
outflows. The data obtained in this study are used in conjunction with Spitzer,
AKARI, and IRAS data. A parsec-scale bipolar outflow is discovered in our H_2
line image, which is supported by the detection in the archival Spitzer images.
The H_2 image exhibits signs of precession of the main jet and shows tentative
evidence for a second outflow. These suggest the possibility of a companion to
the outflow source. There is a strong component of continuum emission in the
direction of the outflow, which supports the idea that the outflow cavity
provides a path for radiation to escape, thereby reducing the radiation
pressure on the accreted matter. The bulk of the emission observed close to the
outflow in the WFCAM and Spitzer bands is rotated counter clockwise with
respect to the outflow traced in H_2, which may be due to precession. The YSO
driving the outflow is identified in the Spitzer images. The spectral energy
distribution (SED) of the YSO is studied using available radiative transfer
models. A model fit to the SED of the central source tells us that the YSO has
a mass of 12.23 M_sun and that it is in an early stage of evolution.Comment: 6 Pages, 5 figures, accepted for publication by Astronomy and
Astrophysic
L & M band infrared studies of V4332 Sagittarii - detection of the water-ice absorption band at 3.05 microns and the CO fundamental band in emission
L and M band observations of the nova-like variable V4332 Sgr are presented.
Two significant results are obtained viz. the unusual detection of water ice at
3.05 microns and the fundamental band of 12CO at 4.67 microns in emission. The
ice feature is a first detection in a nova-like variable while the CO emission
is rarely seen in novae. These results, when considered together with other
existing data, imply that V4332 Sgr could be a young object surrounded by a
circumstellar disc containing gas, dust and ice. The reason for a nova-like
outburst to occur in such a system is unclear. But since planets are believed
to form in such disks, it appears plausible that the enigmatic outburst of
V4332 Sgr could be due to a planetary infall. We also give a more reliable
estimate for an epoch of dust formation around V4332 Sgr which appears to have
taken place rather late in 1999 - nearly five years after its outburst.Comment: 10 pages, 3 figures (to appear in ApJ(Letters), 2004
Remarkable changes in the near-infrared spectrum of the nova-like variable V4332 Sgr
We report on recent near-IR observations of V4332 Sgr - the nova-like
variable that erupted in 1994. Its rapid, post-outburst evolution to a cool M
type giant/supergiant, soon after its outburst, had showed that it was an
unusual object differing from other eruptive variables like classical/symbiotic
novae or born-again AGB stars. The present study of V4332 Sgr was motivated by
the keen interest in the recent eruption of V838 Mon - which along with V4332
Sgr - is believed to belong to a new class of objects (we propose they may be
called "quasi-novae"). Our observations show new developments in the evolution
of V4332 Sgr. The most striking feature is the detection of several molecular
bands of AlO - a rarely seen molecule in astronomical spectra - in the JHK
spectra. Many of these bands are being detected for the first time. The only
other detection of some of these AlO bands are in V838 Mon, thereby showing
further spectral similarities between the two objects. JHK photometry shows the
development of a new dust shell around V4332 Sgr with a temperature of ~ 900K.
This dust shell does not appear to be associated with ejecta of the 1994
outburst but is due to a second mass-loss episode which is not expected in a
classical nova outburst. The cold molecular environment, suggested by the AlO
emission, is also not expected in novae ejecta. We model the AlO bands and also
discuss the possible formation mechanism of the AlO.Comment: To appear in Ap.J(L), 3 figure
The properties of the high-mass star formation region IRAS22475+5939
IRAS22475+5939 has been well researched by previous astronomers. But we still
get some new characteristics about it, using the first observations in lines of
CO J=2-1,13CO J=2-1,13CO J=3-2 by the KOSMA 3 m telescope. The mapping of the
intensity ratio of 13CO J=3-2 and 13CO J=2-1 shows the distribution of the
temperature with two peaks, which don't coincide with IRAS22475+5939 source and
the center of the HII region, but at the edge of the HII region. The overlays
of the Spitzer IRAC 8um and CO contours indicate that they are associated with
each other and the strongest polycyclic aromatic hydrocarbons (PAHs) emission
is at the position of IRAS22475+5939 source. While the IRAS LRS spectrum at
7-23 um and the PHT-s spectrum at 2-12 um of IRAS22475+5939 source also exhibit
strong PAHs emission characters at the main PAH bands. The diversity of PAH
family should be responsible for the plateaus of PAHs emission in the PHT-s
spectrum and the IRAS-LRS spectrum. An analysis and modeling in infrared bands
suggest that IRAS22475+5939 is more likely to be a Class I YSO. Where this is
the case, the star is likely to have a temperature T_{EFF} \sim 9995.8 K, mass
\sim15.34 M_(sun), luminosity \sim 1.54*10^4 L_(sun) and age \sim 1.54*10^4 yr.
The model shows that the circumstellar disc emission is important for the
wavelength between 1 and 10 um, otherwise, envelope fluxes for lambda >10 um.
The bipolar outflow is confirmed in the molecular cloud. The excited star of
the HII region has the chance to be the driving source of the outflow. The high
resolution is required.Comment: 12 pages, 20 figures and 5 tables, Accepted for publication in RA
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