5,937 research outputs found
Evaluation of proposed Skylab and SSP soap products
Three personal hygiene cleansing agents and one laundry detergent (sodium dodecyl benzene sulfonate), which are all candidates for use on long-duration space missions, were evaluated in terms of dermatological effects on human subjects and effects on microbiological species. None of the four materials exhibited adverse dermatological effects from either skin patch tests of two weeks duration or a simulated Skylab personal hygiene regimen of up to four weeks duration. No significant alterations in skin microflora during the use regimen were found. None of the four materials were found to serve as microbiological support media for the species tested, but a species of air-borne mold was observed to grow rapidly in a neutralized aqueous solution. None of the candidate agents was found to be strongly biocidal
Protection of Works of Art From Atmospheric Ozone
Assesses the colorfastness of organic colorants and watercolor pigments tested in atmospheric ozone. A summary of a full report of the Environmental Quality Laboratory, California Institute of Technology, Pasadena
Accurate photometry of extended spherically symmetric sources
We present a new method to derive reliable photometry of extended spherically
symmetric sources from {\it HST} images (WFPC2, ACS/WFC and NICMOS/NIC2
cameras), extending existing studies of point sources and marginally resolved
sources. We develop a new approach to accurately determine intrinsic sizes of
extended spherically symmetric sources, such as star clusters in galaxies
beyond the Local Group (at distances <~ 20 Mpc), and provide a detailed
cookbook to perform aperture photometry on such sources, by determining
size-dependent aperture corrections (ACs) and taking sky oversubtraction as a
function of source size into account. In an extensive Appendix, we provide the
parameters of polynomial relations between the FWHM of various input profiles
and those obtained by fitting a Gaussian profile (which we have used for
reasons of computational robustness, although the exact model profile used is
irrelevant), and between the intrinsic and measured FWHM of the cluster and the
derived AC. Both relations are given for a number of physically relevant
cluster light profiles, intrinsic and observational parameters. AC relations
are provided for a wide range of apertures. Depending on the size of the source
and the annuli used for the photometry, the absolute magnitude of such extended
objects can be underestimated by up to 3 mag, corresponding to an error in mass
of a factor of 15. We carefully compare our results to those from the more
widely used DeltaMag method, and find an improvement of a factor of 3--40 in
both the size determination and the AC.Comment: The paper is accepted for publication in A&A, Section 13
(Observational Techniques, published electronically). The published version
contains one example table per appendix. A version of the paper containing
all tables as well as all data in electronical form are available
http://www.astro.physik.uni-goettingen.de/~galev/panders/Sizes_AC
Dynamical Masses of Young Star Clusters in NGC 4038/4039
In order to estimate the masses of the compact, young star clusters in the
merging galaxy pair, NGC 4038/4039 (``the Antennae''), we have obtained medium
and high resolution spectroscopy using ISAAC on VLT-UT1 and UVES on VLT-UT2 of
five such clusters. The velocity dispersions were estimated using the stellar
absorption features of CO at 2.29 microns and metal absorption lines at around
8500 \AA, including lines of the Calcium Triplet. The size scales and light
profiles were measured from HST images. From these data and assuming Virial
equilibrium, we estimated the masses of five clusters. The resulting masses
range from 6.5 x 10^5 to 4.7 x 10^6 M_sun. These masses are large, factor of a
few to more than 10 larger than the typical mass of a globular cluster in the
Milky Way. The mass-to-light ratios for these clusters in the V- and K-bands in
comparison with stellar synthesis models suggest that to first order the IMF
slopes are approximately consistent with Salpeter for a mass range of 0.1 to
100 M_sun. However, the clusters show a significant range of possible IMF
slopes or lower mass cut-offs and that these variations may correlate with the
interstellar environment of the cluster. Comparison with the results of
Fokker-Planck simulations of compact clusters with properties similar to the
clusters studied here, suggest that they are likely to be long-lived and may
lose a substantial fraction of their total mass. This mass loss would make the
star clusters obtain masses which are comparable to the typical mass of a
globular cluster.Comment: 16 pages, 12 figures, A&A accepte
The Globular Cluster System in the Inner Region of M87
1057 globular cluster candidates have been identified in a WFPC2 image of the
inner region of M87. The Globular Cluster Luminosity Function (GCLF) can be
well fit by a Gaussian profile with a mean value of m_V^0=23.67 +/- 0.07 mag
and sigma=1.39 +/- 0.06 mag (compared to m_V^0=23.74 mag and sigma=1.44 mag
from an earlier study using the same data by Whitmore it et al. 1995). The GCLF
in five radial bins is found to be statistically the same at all points,
showing no clear evidence of dynamical destruction processes based on the
luminosity function (LF), in contradiction to the claim by Gnedin (1997).
Similarly, there is no obvious correlation between the half light radius of the
clusters and the galactocentric distance. The core radius of the globular
cluster density distribution is R_c=56'', considerably larger than the core of
the stellar component (R_c=6.8''). The mean color of the cluster candidates is
V-I=1.09 mag which corresponds to an average metallicity of Fe/H = -0.74 dex.
The color distribution is bimodal everywhere, with a blue peak at V-I=0.95 mag
and a red peak at V-I=1.20 mag. The red population is only 0.1 magnitude bluer
than the underlying galaxy, indicating that these clusters formed late in the
metal enrichment history of the galaxy and were possibly created in a burst of
star/cluster formation 3-6 Gyr after the blue population. We also find that
both the red and the blue cluster distributions have a more elliptical shape
(Hubble type E3.5) than the nearly spherical galaxy. The average half light
radius of the clusters is ~2.5 pc which is comparable to the 3 pc average
effective radius of the Milky Way clusters, though the red candidates are ~20%
smaller than the blue ones.Comment: 40 pages, 17 figures, 4 tables, latex, accepted for publication in
the Ap
The Specific Globular Cluster Frequencies of Dwarf Elliptical Galaxies from the Hubble Space Telescope
The specific globular cluster frequencies (S_N) for 24 dwarf elliptical (dE)
galaxies in the Virgo and Fornax Clusters and the Leo Group imaged with the
Hubble Space Telescope are presented. Combining all available data, we find
that for nucleated dEs --- which are spatially distributed like giant
ellipticals in galaxy clusters --- S_N(dE,N)=6.5 +- 1.2 and S_N increases with
M_V, while for non-nucleated dEs --- which are distributed like late-type
galaxies --- S_N(dE,noN)=3.1 +- 0.5 and there is little or no trend with M_V.
The S_N values for dE galaxies are thus on average significantly higher than
those for late-type galaxies, which have S_N < 1. This suggests that dE
galaxies are more akin to giant Es than to late-type galaxies. If there are
dormant or stripped irregulars hiding among the dE population, they are likely
to be among the non-nucleated dEs. Furthermore, the similarities in the
properties of the globular clusters and in the spatial distributions of dE,Ns
and giant Es suggest that neither galaxy mass or galaxy metallicity is
responsible for high values of S_N. Instead, most metal-poor GCs may have
formed in dwarf-sized fragments that merged into larger galaxies.Comment: 12 pages (uses aaspp4.sty), 2 figures, 1 table, to appear in the
Astrophysical Journa
The Star Cluster Population of M51: II. Age distribution and relations among the derived parameters
We use archival {\it Hubble Space Telescope} observations of broad-band
images from the ultraviolet (F255W-filter) through the near infrared (NICMOS
F160W-filter) to study the star cluster population of the interacting spiral
galaxy M51. We obtain age, mass, extinction, and effective radius estimates for
1152 star clusters in a region of kpc centered on the
nucleus and extending into the outer spiral arms. In this paper we present the
data set and exploit it to determine the age distribution and relationships
among the fundamental parameters (i.e. age, mass, effective radius). Using this
dataset we find: {\it i}) that the cluster formation rate seems to have had a
large increase 50-70 Myr ago, which is coincident with the suggested
{\it second passage} of its companion, NGC 5195, {\it ii}) a large number of
extremely young ( 10 Myr) star clusters, which we interpret as a population
of unbound clusters of which a large majority will disrupt within the next
10 Myr, and {\it iii)} that the distribution of cluster sizescan be well
approximated by a power-law with exponent, , which is
very similar to that of Galactic globular clusters, indicating that cluster
disruption is largely independent of cluster radius. In addition, we have used
this dataset to search for correlations among the derived parameters. In
particular, we do not find any strong trends between the age and mass, mass and
effective radius, nor between the galactocentric distance and effective radius.
There is, however, a strong correlation between the age of a cluster and its
extinction, with younger clusters being more heavily reddened than older
clusters.Comment: 21 pages, 20 figures, accepted A&
- âŠ