1,078 research outputs found
Identifying Contaminated K-band Globular Cluster RR Lyrae Photometry
Acquiring near-infrared K-band (2.2 um) photometry for RR Lyrae variables in
globular clusters and nearby galaxies is advantageous since the resulting
distances are less impacted by reddening and metallicity. However, K-band
photometry for RR Lyrae variables in M5, Reticulum, M92, omega Cen, and M15
display clustercentric trends. HST ACS data imply that multiple stars in close
proximity to RR Lyrae variables located near the cluster core, where the
stellar density increases markedly, are generally unresolved in ground-based
images. RR Lyrae variables near the cluster cores appear to suffer from
photometric contamination, thereby yielding underestimated cluster distances
and biased ages. The impact is particularly pernicious since the contamination
propagates a systematic uncertainty into the distance scale, and hinders the
quest for precision cosmology. The clustercentric trends are probably
unassociated with variations in chemical composition since an empirical K-band
period-magnitude relation inferred from Araucaria/VLT data for RR Lyrae
variables in the Sculptor dSph exhibits a negligible metallicity dependence:
(0.059+-0.095)[Fe/H], a finding that supports prior observational results. A
future multi-epoch high-resolution near-infrared survey, analogous to the
optical HST ACS Galactic Globular Cluster Survey, may be employed to establish
K-band photometry for the contaminating stars discussed here.Comment: To appear in PAS
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New ammonia masers towards NGC6334I
We report the detection of new ammonia masers in the non-metastable (8,6) and
(11,9) transitions towards the massive star forming region NGC6334I.
Observations were made with the ATCA interferometer and the emitting region
appears unresolved in the 2.7" x 0.8" beam, with deconvolved sizes less than an
arcsecond. We estimate peak brightness temperatures of 7.8 x 10^5 and 1.2 x
10^5 K for the (8,6) and (11,9) transitions, respectively. The masers appear
coincident both spatially and in velocity with a previously detected ammonia
(6,6) maser. We also suggest that emission in the (10,9), (9,9) and (7,6)
transitions may also be masers, based on their narrow line widths and
overlapping velocity ranges with the above masers, as observed with the
single-dish Mopra radiotelescope
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Hot high-mass accretion disk candidates
To better understand the physical properties of accretion disks in high-mass
star formation, we present a study of a 12 high-mass accretion disk candidates
observed at high spatial resolution with the Australia Telescope Compact Array
(ATCA) in the NH3 (4,4) and (5,5) lines. Almost all sources were detected in
NH3, directly associated with CH3OH Class II maser emission. From the remaining
eleven sources, six show clear signatures of rotation and/or infall motions.
These signatures vary from velocity gradients perpendicular to the outflows, to
infall signatures in absorption against ultracompact HII regions, to more
spherical infall signatures in emission. Although our spatial resolution is
~1000AU, we do not find clear Keplerian signatures in any of the sources.
Furthermore, we also do not find flattened structures. In contrast to this, in
several of the sources with rotational signatures, the spatial structure is
approximately spherical with sizes exceeding 10^4 AU, showing considerable
clumpy sub-structure at even smaller scales. This implies that on average
typical Keplerian accretion disks -- if they exist as expected -- should be
confined to regions usually smaller than 1000AU. It is likely that these disks
are fed by the larger-scale rotating envelope structure we observe here.
Furthermore, we do detect 1.25cm continuum emission in most fields of view.Comment: 21 pages, 32 figures, accepted for ApJS. A high-resolution version
can be found at http://www.mpia.de/homes/beuther/papers.htm
Addressing environmental and atmospheric challenges for capturing high-precision thermal infrared data in the field of astro-ecology
Using thermal infrared detectors mounted on drones, and applying techniques
from astrophysics, we hope to support the field of conservation ecology by
creating an automated pipeline for the detection and identification of certain
endangered species and poachers from thermal infrared data. We test part of our
system by attempting to detect simulated poachers in the field. Whilst we find
that we can detect humans hiding in the field in some types of terrain, we also
find several environmental factors that prevent accurate detection, such as
ambient heat from the ground, absorption of infrared emission by the
atmosphere, obscuring vegetation and spurious sources from the terrain. We
discuss the effect of these issues, and potential solutions which will be
required for our future vision for a fully automated drone-based global
conservation monitoring system.Comment: Published in Proceedings of SPIE Astronomical Telescopes and
Instrumentation 2018. 8 pages, 3 figure
Maser Source Finding Methods in HOPS
The {\bf H}{\bf O} Southern Galactic {\bf P}lane {\bf S}urvey (HOPS) has
observed 100 square degrees of the Galactic plane, using the Mopra radio
telescope to search for emission from multiple spectral lines in the 12\,mm
band (19.5\,--\,27.5\,GHz). Perhaps the most important of these spectral lines
is the 22.2\,GHz water maser transition. We describe the methods used to
identify water maser candidates and subsequent confirmation of the sources. Our
methods involve a simple determination of likely candidates by searching peak
emission maps, utilising the intrinsic nature of water maser emission -
spatially unresolved and spectrally narrow-lined. We estimate completeness
limits and compare our method with results from the {\sc Duchamp} source
finder. We find that the two methods perform similarly. We conclude that the
similarity in performance is due to the intrinsic limitation of the noise
characteristics of the data. The advantages of our method are that it is
slightly more efficient in eliminating spurious detections and is simple to
implement. The disadvantage is that it is a manual method of finding sources
and so is not practical on datasets much larger than HOPS, or for datasets with
extended emission that needs to be characterised. We outline a two-stage method
for the most efficient means of finding masers, using {\sc Duchamp}.Comment: 8 pages, 1 table, 4 figures. Accepted for publication in PASA special
issue on Source Finding & Visualisatio
Stellar Populations of the Sagittarius Dwarf Irregular Galaxy
We present deep BVRI CCD photometry of the stars in the dwarf irregular
galaxy SagDIG. The color-magnitude diagrams of the measured stars in SagDIG
show a blue plume which consists mostly of young stellar populations, and a
well-defined red giant branch (RGB). The foreground reddening of SagDIG is
estimated to be E(B-V)=0.06. The tip of the RGB is found to be at
I_(TRGB)=21.55 +/- 0.10 mag. From this the distance to this galaxy is estimated
to be d = 1.18 +/- 0.10 Mpc. This result, combined with its velocity
information, shows that it is a member of the Local Group. The mean metallicity
of the red giant branch is estimated to be [Fe/H] < -2.2 dex. This shows that
SagDIG is one of the most metal-poor galaxies. Total magnitudes of SagDIG (<
r_H (= 107 arcsec)) are derived to be B^T=13.99 mag, V^T=13.58 mag, R^T=13.19
mag, and I^T=12.88 mag, and the corresponding absolute magnitudes are
M_B=-11.62 mag, M_V=-11.97 mag, M_R=-12.33 mag, and M_I=-12.60 mag. Surface
brightness profiles of the central part of SagDIG are approximately fit by a
King model with a core concentration parameter c = log (r_t / r_c) ~ 0.6, and
those of the outer part follow an exponential law with a scale length of 37
arcsec. The central surface brightness is measured to be mu_B (0) = 24.21 mag
arcsec^(-2) and mu_V (0) =23.91 mag arcsec^(-2). The magnitudes and colors of
the brightest blue and red stars in SagDIG (BSG and RSG) are measured to be,
respectively, _BSG = 19.89 +/- 0.13 mag, _BSG = 0.08 +/- 0.07
mag, _RSG = 20.39 +/- 0.10 mag, and _RSG = 1.29 +/- 0.12 mag.
The corresponding absolute magnitudes are derived to be _BSG = -5.66
mag and _RSG = -5.16 mag, which are about one magnitude fainter than
those expected from conventional correlations with galaxy luminosity.Comment: 16 pages(AASLaTeX), 10 Postscript figures, Accepted for publication
in Astronomical Journal, 200
VLASSICK: The VLA Sky Survey in the Central Kiloparsec
At a distance of 8 kpc, the center of our Galaxy is the nearest galactic
nucleus, and has been the subject of numerous key projects undertaken by great
observatories such as Chandra, Spitzer, and Herschel. However, there are still
no surveys of molecular gas properties in the Galactic center with less than
30" (1 pc) resolution. There is also no sensitive polarization survey of this
region, despite numerous nonthermal magnetic features apparently unique to the
central 300 parsecs. In this paper, we outline the potential the VLASS has to
fill this gap. We assess multiple considerations in observing the Galactic
center, and recommend a C-band survey with 10 micro-Jy continuum RMS and
sensitive to molecular gas with densities greater than 10^4 cm^{-3}, covering
17 square degrees in both DnC and CnB configurations ( resolution ~5"),
totaling 750 hours of observing time. Ultimately, we wish to note that the
upgraded VLA is not just optimized for fast continuum surveys, but has a
powerful correlator capable of simultaneously observing continuum emission and
dozens of molecular and recombination lines. This is an enormous strength that
should be fully exploited and highlighted by the VLASS, and which is ideally
suited for surveying the center of our Galaxy.Comment: 13 pages, 3 figures, a White Paper submitted to provide input in
planning the Very Large Array Sky Surve
Image Dependency In The Recognition Of Newly Learnt Faces
Research investigating the effect of lighting and viewpoint changes on unfamiliar and newly learnt faces has revealed that such recognition is highly image dependent and that changes in either of these leads to poor recognition accuracy. Three experiments are reported to extend these findings by examining the effect of apparent age on the recognition of newly learnt faces. Experiment 1 investigated the ability to generalize to novel ages of a face after learning a single image. It was found that recognition was best for the learnt image with performance falling the greater the dissimilarity between the study and test images. Experiments 2 and 3 examined whether learning two images aids subsequent recognition of a novel image. The results indicated that interpolation between two studied images (Experiment 2) provided some additional benefit over learning a single view, but that this did not extend to extrapolation (Experiment 3). The results from all studies suggest that recognition was driven primarily by pictorial codes and that the recognition of faces learnt from a limited number of sources operates on stored images of faces as opposed to more abstract, structural, representations. </jats:p
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