102 research outputs found
Dust around Mira variables: An analysis of IRAS LRS spectra
The spatial extent and spectral appearance of the thin dust shell around Mira variables is determined largely by the dust absorptivity, Q(sub abs)(lambda), and the dust condensation temperature T(sub cond). Both Q(sub abs)(lambda) and T(sub cond) are extracted from IRAS low-resolution spectra (LRS) spectra. In order to do this, the assumption that the ratio of total power in the 10 micron feature to that in the 20 micron feature should be equal to that measured in other amorphous silicates (e.g., synthesized amorphous Mg2SiO4). It was found that T(sub cond) decreases with decreasing strength of the 10 micron feature, from T(sub cond) = 1000 K to 500 K (estimated error 20 percent). A value for the near-infrared dust absorptivity could not be determined. Although this parameter strongly affects the condensation radius, it hardly affects the shape of the LRS spectrum (as long as the optically thin approximation is valid), because it scales the spatial distribution of the dust. Information on the magnitude of the near-infrared dust absorptivity may be deduced from the unique carbon star BM Gem. This star has a LRS spectrum with silicate features indication an inner dust shell temperature of at least 1000 K. However, on the basis of observations in the 1920s-30s one may infer an inner dust shell radius of at least 6x10(exp 12)m. To have this high temperature at such a large distance, the near-infrared absorptivity of the dust must be high
Near infrared nadir retrieval of vertical column densities: methodology and application to SCIAMACHY
Nadir observations with the shortwave infrared channels of SCIAMACHY on-board the ENVISAT satellite can be used to derive information on atmospheric gases such as CO, CH<sub>4</sub>, N<sub>2</sub>O, CO<sub>2</sub>, and H<sub>2</sub>O. For the operational level 1b-2 processing of SCIAMACHY data, a new retrieval code BIRRA (Beer InfraRed Retrieval Algorithm) has been developed. BIRRA performs a nonlinear or separable least squares fit (with bound constraints optional) of the measured radiance, where molecular concentration vertical profiles are scaled to fit the observed data. Here we present the forward modeling (radiative transfer) and inversion (least squares optimization) fundamentals of the code along with the further processing steps required to generate higher level products such as global distributions and time series. Moreover, various aspects of level 1 (observed spectra) and auxiliary input data relevant for successful retrievals are discussed. BIRRA is currently used for operational analysis of carbon monoxide vertical column densities from SCIAMACHY channel 8 observations, and is being prepared for methane retrievals using channel 6 spectra. A set of representative CO retrievals and first CH<sub>4</sub> results are presented to demonstrate BIRRA's capabilities
ESO Imaging survey: Optical Deep Public Survey
This paper presents new five passbands (UBVRI) optical wide-field imaging
data accumulated as part of the DEEP Public Survey (DPS) carried out as a
public survey by the ESO Imaging Survey (EIS) project. Out of the 3 square
degrees originally proposed, the survey covers 2.75 square degrees, in at least
one band (normally R), and 1.00 square degrees in five passbands. The median
seeing, as measured in the final stacked images, is 0.97", ranging from 0.75"
to 2.0". The median limiting magnitudes (AB system, 2" aperture, 5 sigma
detection limit) are U_(AB)=25.65, B_(AB)=25.54, V_(AB)=25.18, R_(AB) = 24.8
and I_(AB)=24.12 mag, consistent with those proposed in the original survey
design. The paper describes the observations and data reduction using the EIS
Data Reduction System and its associated EIS/MVM library. The quality of the
individual images were inspected, bad images discarded and the remaining used
to produce final image stacks in each passband, from which sources have been
extracted. Finally, the scientific quality of these final images and associated
catalogs was assessed qualitatively by visual inspection and quantitatively by
comparison of statistical measures derived from these data with those of other
authors as well as model predictions, and from direct comparison with the
results obtained from the reduction of the same dataset using an independent
(hands-on) software system. Finally to illustrate one application of this
survey, the results of a preliminary effort to identify sub-mJy radio sources
are reported. To the limiting magnitude reached in the R and I passbands the
success rate ranges from 66 to 81% (depending on the fields). These data are
publicly available at CDS.Comment: 24 pages, 26 figures. Accepted for pubblication in A&
ESO Imaging Survey VII. Distant Cluster Candidates over 12 square degrees
In this paper the list of candidate clusters identified from the I-band data
of the ESO Imaging Survey (EIS) is completed using the images obtained over a
total area of about 12 square degrees. Together with the data reported earlier
the total I-band coverage of EIS is 17 square degrees, which has yielded a
sample of 252 cluster candidates in the redshift range 0.2 \lsim z \lsim 1.3.
This is the largest optically-selected sample currently available in the
Southern Hemisphere. It is also well distributed in the sky thus providing
targets for a variety of VLT programs nearly year round.Comment: 5 pages, 3 figures, submitted to Astronomy & Astrophysic
ESO Imaging Survey: Infrared Deep Public Survey
This paper presents new J and Ks data obtained from observations conducted at
the ESO 3.5m New Technology Telescope using the SOFI camera. These data were
taken as part of the ESO Imaging Survey Deep Public Survey (DPS) and
significantly extend the earlier optical/infrared EIS-DEEP survey presented in
a previous paper. The DPS-IR survey comprises two observing strategies: shallow
Ks observations providing nearly full coverage of pointings with complementary
multi-band optical data and deeper J and Ks observations of the central parts
of these fields. The DPS-IR survey provides a coverage of roughly 2.1 square
degrees in Ks with 0.63 square degrees to fainter magnitudes and also covered
in J, over three independent regions of the sky. The goal of the present paper
is to describe the observations, the data reduction procedures, and to present
the final survey products. The astrometric solution with an estimated accuracy
of <0.15" is based on the USNO catalog. The final stacked images presented here
number 89 and 272, in J and Ks, respectively, the latter reflecting the larger
surveyed area. The J and Ks images were taken with a median seeing of 0.77" and
0.8". The images reach a median 5sigma limiting magnitude of J_AB~23.06 in an
aperture of 2", while the corresponding limiting magnitude in Ks_AB is ~21.41
and ~22.16 mag for the shallow and deep strategies. Overall, the observed
limiting magnitudes are consistent with those originally proposed. The quality
of the data has been assessed by comparing the measured magnitude of sources at
the bright end directly with those reported by the 2MASS survey and at the
faint end by comparing the counts of galaxies and stars with those of other
surveys to comparable depth and to model predictions. The final science-grade
catalogs and images are available at CDS.Comment: Accepted for publication in A&A, 14 pages, 8 figures, a full
resolution version of the paper is available from
http://www.astro.ku.dk/~lisbeth/eisdata/papers/5019.pd
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