33 research outputs found
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
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
JHK Observations of Faint Standard Stars in the Mauna Kea Near-Infrared Photometric System
JHK photometry in the Mauna Kea Observatory (MKO) near-IR system is presented
for 115 stars. Of these, 79 are UKIRT standards and 42 are LCO standards. The
average brightness is 11.5 mag, with a range of 10 to 15. The average number of
nights each star was observed is 4, and the average of the internal error of
the final results is 0.011 mag. These JHK data agree with those reported by
other groups to 0.02 mag. The measurements are used to derive transformations
between the MKO JHK photometric system and the UKIRT, LCO and 2MASS systems.
The 2MASS-MKO data scatter by 0.05 mag for redder stars: 2MASS-J includes H2O
features in dwarfs and MKO-K includes CO features in giants. Transformations
derived for stars whose spectra contain only weak features cannot give accurate
transformations for objects with strong absorption features within a filter
bandpasses. We find evidence of systematic effects at the 0.02 mag level in the
photometry of stars with J<11 and H,K<10.5. This is due to an underestimate of
the linearity correction for stars observed with the shortest exposure times;
very accurate photometry of stars approaching the saturation limits of infrared
detectors which are operated in double-read mode is difficult to obtain. Four
stars in the sample, GSPC S705-D, FS 116 (B216-b7), FS 144 (Ser-EC84) and FS 32
(Feige 108), may be variable. 84 stars in the sample have 11< J< 15 and
10.5<H,K<15, are not suspected to be variable, and have magnitudes with an
estimated error <0.027 mag; 79 of these have an error of <0.020 mag. These
represent the first published high-accuracy JHK stellar photometry in the MKO
photometric system; we recommend these objects be employed as primary standards
for that system [abridged].Comment: Accepted for publication in MNRAS, 14 pages, 5 Figure
UWISH2 -- The UKIRT Widefield Infrared Survey for H2
We present the goals and preliminary results of an unbiased, near-infrared,
narrow-band imaging survey of the First Galactic Quadrant (10deg<l<65deg ;
-1.3deg<b<+1.3deg). This area includes most of the Giant Molecular Clouds and
massive star forming regions in the northern hemisphere. The survey is centred
on the 1-0S(1) ro-vibrational line of H2, a proven tracer of hot, dense
molecular gas in star-forming regions, around evolved stars, and in supernova
remnants. The observations complement existing and upcoming photometric surveys
(Spitzer-GLIMPSE, UKIDSS-GPS, JCMT-JPS, AKARI, Herschel Hi-GAL, etc.), though
we probe a dynamically active component of star formation not covered by these
broad-band surveys. Our narrow-band survey is currently more than 60% complete.
The median seeing in our images is 0.73arcsec. The images have a 5sigma
detection limit of point sources of K=18mag and the surface brightness limit is
10^-19Wm^-2arcsec^-2 when averaged over our typical seeing. Jets and outflows
from both low and high mass Young Stellar Objects are revealed, as are new
Planetary Nebulae and - via a comparison with earlier K-band observations
acquired as part of the UKIDSS GPS - numerous variable stars. With their
superior spatial resolution, the UWISH2 data also have the potential to reveal
the true nature of many of the Extended Green Objects found in the GLIMPSE
survey.Comment: 14pages, 8figures, 2tables, accepted for publication by MNRAS, a
version with higher resolution figures can be found at
http://astro.kent.ac.uk/~df
Orbitally modulated dust formation by the WC7+O5 colliding-wind binary WR140
We present high-resolution infrared (2--18 micron) images of the archetypal
periodic dust-making Wolf-Rayet binary system WR140 (HD 193793) taken between
2001 and 2005, and multi-colour (J -- [19.5]) photometry observed between 1989
and 2001. The images resolve the dust cloud formed by WR140 in 2001, allowing
us to track its expansion and cooling, while the photometry allows tracking the
average temperature and total mass of the dust. The combination of the two
datasets constrains the optical properties of the dust. The most persistent
dust features, two concentrations at the ends of a `bar' of emission to the
south of the star, were observed to move with constant proper motions of
324+/-8 and 243+/-7 mas/y. Longer wavelength (4.68-micron and 12.5-micron)
images shows dust emission from the corresponding features from the previous
(1993) periastron passage and dust-formation episode. A third persistent dust
concentration to the east of the binary (the `arm') was found to have a proper
motion ~ 320 mas/y. Extrapolation of the motions of the concentrations back to
the binary suggests that the eastern `arm' began expansion 4--5 months earlier
than those in the southern `bar', consistent with the projected rotation of the
binary axis and wind-collision region (WCR) on the sky. Comparison of model
dust images and the observations constrain the intervals when the WCR was
producing sufficiently compressed wind for dust nucleation in the WCR, and
suggests that the distribution of this material was not uniform about the axis
of the WCR, but more abundant in the following edge in the orbital plane.Comment: 21 pages, 10 figures, accepted for MNRAS. A version with higher
resolution figures is available at
ftp://ftp.roe.ac.uk/pub/pmw/wr140dust.ps.g
The UKIRT Hemisphere Survey: Definition and Full J-band Data Release
This paper defines the UK Infra-red Telescope (UKIRT) Hemisphere Survey (UHS) and release of the complete J-band dataset. The UHS provides continuous coverage in the northern hemisphere from a declination of 0 deg to 60 deg by combining the existing Large Area Survey, Galactic Plane Survey and Galactic Clusters Survey conducted under the UKIRT Infra-red Deep Sky Survey (UKIDSS) programme with a new additional ~12,700 sq.deg area not covered by UKIDSS. This data release includes J-band imaging and source catalogues over the new area, which, together with UKIDSS, completes the J-band UHS coverage over the full ~17,900 sq.deg area. 98 per cent of the data in this release have passed quality control criteria, the remaining 2 per cent being scheduled for re-observation. The median 5-sigma point source sensitivity of the released data is 19.6 mag (Vega). The median full width at half-maximum of the point spread function across the dataset is 0.75 arcsec. In this paper, we outline the survey management, data acquisition, processing and calibration, quality control and archiving as well as summarising the characteristics of the released data products. The data are initially available to a limited consortium with a world-wide release scheduled for August 2018
Extreme infrared variables from UKIDSS-I. A concentration in star-forming regions
We present initial results of the first panoramic search for high-amplitude near-infrared variability in theGalactic plane.We analyse the widely separated two-epoch K-band photometry in the fifth and seventh data releases of the UKIDSS Galactic plane survey.We find 45 stars with δK > 1 mag, including two previously known OH/IR stars and a Nova. Even though the midplane is not yet included in the data set, we find the majority (66 per cent) of our sample to be within known star-forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (12 stars). Sources in SFRs show spectral energy distributions that support classification as young stellar objects (YSOs). This indicates that YSOs dominate the Galactic population of high-amplitude infrared variable stars at low luminosities and therefore likely dominate the total high-amplitude population. Spectroscopic follow up of the DR5 sample shows at least four stars with clear characteristics of eruptive premain- sequence variables, two of which are deeply embedded. Our results support the recent concept of eruptive variability comprising a continuum of outburst events with different timescales and luminosities, but triggered by a similar physical mechanism involving unsteady accretion. Also, we find what appears to be one of the most variable classical Be stars. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society