20 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
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
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
A search for radioactive 26Al in the nova-like variable V4332 Sagittarii
We have searched for the important radioactive isotope 26Al in the nova-like
source V4332 Sgr. Recent results from gamma ray astronomy show that there is
pervasive emission of the 1.809 MeV gamma ray photon, arising from the decay of
26Al to 26Mg, from all over the galactic plane. Though the sites from where
this emission originates are not clearly established, novae are believed to be
an important contributing source. In this context, V4332 Sgr presented a rare
opportunity to observationally investigate whether novae or novae-like sources
synthesize 26Al and to what extent. Strong AlO bands in the near-IR have been
reported in this object recently. As molecular bands of different isotopic
compositions are readily resolved spectroscopically (e.g. 12CO and 13CO), it
was thought that the components of AlO associated with
26Al and stable 27Al could be detected as separate bands. Our spectra
indicate that there is no strong presence of 26Al in V4332 Sgr. A reliable
upper limit of 0.10 for the 26Al/27Al ratio is determined which constitutes the
first observational constraint for this ratio in a potential 26Al producing
source. While V4332 Sgr is not a typical nova, its outburst amplitude and
light-curve behaviour bear close similarity to that of novae. Hence, although
the results from V4332 Sgr cannot be directly extended to novae in general, the
limit on the observed 26Al/27Al ratio could be a useful input in constraining
rather uncertain nucleosynthesis models for the production of 26Al in
novae/novae-like sources. By comparing the observed 26Al/27Al ratio in V4332
Sgr with that expected in classical novae it appears unlikely that the
progenitor of V4332 Sgr is an Oxygen-Neon-Magnesium white dwarf.Comment: 9 pages, 2 figures, to appear in Ap.J(L) July 200
UKIRT Widefield Infrared Survey for Fe+
The United Kingdom Infrared Telescope (UKIRT)Widefield Infrared Survey for Fe+ (UWIFE) is a 180 deg2 imaging survey of the first Galactic quadrant (7° < l < 62° |b| <1°.5) that uses a narrow-band filter centred on the [Fe II] 1.644-μm emission line. The [Fe II] 1.644-μm emission is a good tracer of dense, shock-excited gas, and the survey will probe violent environments around stars: star-forming regions, evolved stars, and supernova remnants, among others. The UWIFE survey is designed to complement the existing UKIRTW idefield Infrared Survey for H2 (UWISH2). The survey will also complement existing broad-band surveys. The observed images have a nominal 5Ï? detection limit of 18.7 mag for point sources, with a median seeing of 0.83 arcsec. For extended sources, we estimate a surface brightness limit of 8.1 Ã? 10-20 W m-2 arcsec-2. In this paper, we present an overview and some preliminary results of this survey. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Near IR Spectroscopic monitoring of WR 140 during the 2001 periastron passage
We present new spectra of WR 140 (HD 193793) in the JHK bands with some
covering the 1.083-micron He I emission line at higher resolution, observed
between 2000 October and 2003 May to cover its 2001 periastron passage. The WC7
+ O4-5 spectroscopic binary WR 140 is the prototype of colliding-wind, episodic
dust-making Wolf-Rayet systems which also show strong variations in radio and
X-ray emission. The JHK spectra showed changes in continuum and in the
equivalent widths of the WC emission lines, consistent with formation of dust
starting between 2001 January 3 and March 26 (orbital phases 0.989 and 0.017)
and its subsequent fading and cooling. The 1.083-micron He I line has a P-Cygni
profile which showed variations in both absorption and emission components as
WR 140 went through periastron passage. The variation of the absorption
component yielded tight constraints on the geometry of the wind-collision
region, giving theta = 50 +/- 8 degrees for the opening semi-angle of the
interaction `cone', indicating a wind-momentum ratio of the O to the WR
star=0.1, about three times larger than previously believed. As the system
approached periastron, the emission component showed the appearance of a
significant sub-peak, movement of which across the profile was seen to be
consistent with its formation in wind material flowing along the contact
discontinuity between the two stellar winds and the changing orientation of the
colliding wind region. The flux carried in the sub-peak exceeded the X-ray
fluxes measured at previous periastron passages. This additional source of
radiative cooling of the shock-heated gas probably causes it to depart from
being adiabatic around periastron passage, thereby accounting for the departure
of the X-ray flux from its previously expected -dependency.Comment: Accepted for publication in MNRAS - 13 Pages, 10 figure
Extended ionized fe objects in the UWIFE survey
We explore systematically the shocked gas in the first Galactic quadrant of the Milky Way using the United Kingdom Infrared Telescope (UKIRT) Wide-field Infrared Survey for Fe+ (UWIFE). The UWIFE survey is the first imaging survey of the Milky Way in the [Fe ii] 1.644 µm emission line and covers the Galactic plane in the first Galactic quadrant (7◦ < l < 62◦; |b| ≲ 1.◦5). We identify 204 extended ionized Fe objects (IFOs) using a combination of a manual and automatic search. Most of the IFOs are detected for the first time in the [Fe ii] 1.644 µm line. We present a catalog of the measured sizes and fluxes of the IFOs and searched for their counterparts by performing positional cross-matching with known sources. We found that IFOs are associated with supernova remnants (25), young stellar objects (100), Hii regions (33), planetary nebulae (17), and luminous blue variables (4). The statistical and morphological properties are discussed for each of these