2,456 research outputs found
Search for IR Emission from Intracluster Dust in A2029
We have searched for IR emission from the intracluster dust (ICD) in the
galaxy cluster A2029. Weak signals of enhanced extended emission in the cluster
are detected at both 24 and 70 micron. However, the signals are
indistinguishable from the foreground fluctuations. The 24 versus 70 micron
color map does not discriminate the dust emission in the cluster from the
cirrus emission. After excluding the contamination from the point sources, we
obtain upper limits for the extended ICD emission in A2029, 5 x 10^3 Jy/sr at
24 micron and 5 x 10^4 Jy/sr at 70 micron. The upper limits are generally
consistent with the expectation from theoretical calculations and support a
dust deficiency in the cluster compared to the ISM in our galaxy. Our results
suggest that even with the much improved sensitivity of current IR telescopes,
a clear detection of the IR emission from ICD may be difficult due to cirrus
noise.Comment: 5 pages, 4 figures, accepted by ApJ
Disc galaxies with multiple triaxial structures. II. JHK surface photometry and numerical simulations
We present detailed JHK surface photometry with ellipse fits of 13 galaxies
selected from previous optical observations as likely candidates for having a
secondary bar or a triaxial bulge within the primary bar. We have found 7
double-barred galaxies, 3 double-barred galaxies with an additional
intermediate structure with twisted isophotes, and 3 galaxies with a bar and
central twisted isophotes. A global analysis of the structural parameter
characteristics in the I- and K-bands is presented. Various numerical models of
galaxies with bars within bars are also analysed using the ellipse fitting
technique and compared to the observations. A thorough review of the possible
hypotheses able to explain this phenomenon is given with emphasis on the most
likely ones.Comment: 12 pages, AATEX. Accepted for publication in A&A. Large color
postscript figures omitted (Figs. 1), figures 2-9 included; gzip'ed
postscript files of the paper and Figs. 1 available via anonymous ftp at
ftp://obsftp.unige.ch/pub/fri/aasjhk/ , files fri_aasjhk.ps.gz and ngc*.ps.g
A Comprehensive Dust Model Applied to the Resolved Beta Pictoris Debris Disk from Optical to Radio Wavelengths
We investigate whether varying the dust composition (described by the optical
constants) can solve a persistent problem in debris disk modeling--the
inability to fit the thermal emission without over-predicting the scattered
light. We model five images of the beta Pictoris disk: two in scattered light
from HST/STIS at 0.58 microns and HST/WFC3 at 1.16 microns, and three in
thermal emission from Spitzer/MIPS at 24 microns, Herschel/PACS at 70 microns,
and ALMA at 870 microns. The WFC3 and MIPS data are published here for the
first time. We focus our modeling on the outer part of this disk, consisting of
a parent body ring and a halo of small grains. First, we confirm that a model
using astronomical silicates cannot simultaneously fit the thermal and
scattered light data. Next, we use a simple, generic function for the optical
constants to show that varying the dust composition can improve the fit
substantially. Finally, we model the dust as a mixture of the most plausible
debris constituents: astronomical silicates, water ice, organic refractory
material, and vacuum. We achieve a good fit to all datasets with grains
composed predominantly of silicates and organics, while ice and vacuum are, at
most, present in small amounts. This composition is similar to one derived from
previous work on the HR 4796A disk. Our model also fits the thermal SED,
scattered light colors, and high-resolution mid-IR data from T-ReCS for this
disk. Additionally, we show that sub-blowout grains are a necessary component
of the halo.Comment: 23 pages, 20 figures, accepted to Ap
The Content of Several Measures of Social Desirability
The question of whether to remove socially desirable responding (SDR) variance from self-report personality inventories, or to treat it as a facet of personality, has been the center of a debate spanning the last 25 years (Furnham, 1986). Recently, this controversy again came to the forefront of the literature via an exchange between a group of researchers (Block, 1990; Edwards, 1990; Nicholson & Hogan, 1990; Walsh, 1990). The essence of this debate is whether the correlation between a SDR scale and a personality scale indicated that the personality scale is contaminated by SDR bias, or if it merely indicates that there is content overlap between the two types of scales
What Sets the Radial Locations of Warm Debris Disks?
The architectures of debris disks encode the history of planet formation in
these systems. Studies of debris disks via their spectral energy distributions
(SEDs) have found infrared excesses arising from cold dust, warm dust, or a
combination of the two. The cold outer belts of many systems have been imaged,
facilitating their study in great detail. Far less is known about the warm
components, including the origin of the dust. The regularity of the disk
temperatures indicates an underlying structure that may be linked to the water
snow line. If the dust is generated from collisions in an exo-asteroid belt,
the dust will likely trace the location of the water snow line in the
primordial protoplanetary disk where planetesimal growth was enhanced. If
instead the warm dust arises from the inward transport from a reservoir of icy
material farther out in the system, the dust location is expected to be set by
the current snow line. We analyze the SEDs of a large sample of debris disks
with warm components. We find that warm components in single-component systems
(those without detectable cold components) follow the primordial snow line
rather than the current snow line, so they likely arise from exo-asteroid
belts. While the locations of many warm components in two-component systems are
also consistent with the primordial snow line, there is more diversity among
these systems, suggesting additional effects play a role
The Decay of Debris Disks around Solar-Type Stars
We present a Spitzer MIPS study of the decay of debris disk excesses at 24
and 70 m for 255 stars of types F4 - K2. We have used multiple tests,
including consistency between chromospheric and X-ray activity and placement on
the HR diagram, to assign accurate stellar ages. Within this spectral type
range, at 24 m, of the stars younger than 5 Gyr have
excesses at the 3 level or more, while none of the older stars do,
confirming previous work. At 70 m, of the younger stars
have excesses at 3 significance, while only
% of the older stars do. To characterize the far infrared
behavior of debris disks more robustly, we double the sample by including stars
from the DEBRIS and DUNES surveys. For the F4 - K4 stars in this combined
sample, there is only a weak (statistically not significant) trend in the
incidence of far infrared excess with spectral type (detected fractions of
21.9, late F; 16.5, G; and
16.9, early K). Taking this spectral type range together,
there is a significant decline between 3 and 4.5 Gyr in the incidence of
excesses with fractional luminosities just under . There is an
indication that the timescale for decay of infrared excesses varies roughly
inversely with the fractional luminosity. This behavior is consistent with
theoretical expectations for passive evolution. However, more excesses are
detected around the oldest stars than is expected from passive evolution,
suggesting that there is late-phase dynamical activity around these stars.Comment: 46 pages. 7 figures. Accepted to Ap
The first 40 million years of circumstellar disk evolution: the signature of terrestrial planet formation
We characterize the first 40 Myr of evolution of circumstellar disks through
a unified study of the infrared properties of members of young clusters and
associations with ages from 2 Myr up to ~ 40 Myr: NGC 1333, NGC 1960, NGC 2232,
NGC 2244, NGC 2362, NGC 2547, IC 348, IC 2395, IC 4665, Chamaeleon I, Orion
OB1a and OB1b, Taurus, the \b{eta} Pictoris Moving Group, \r{ho} Ophiuchi, and
the associations of Argus, Carina, Columba, Scorpius-Centaurus, and
Tucana-Horologium. Our work features: 1.) a filtering technique to flag noisy
backgrounds, 2.) a method based on the probability distribution of deflections,
P(D), to obtain statistically valid photometry for faint sources, and 3.) use
of the evolutionary trend of transitional disks to constrain the overall
behavior of bright disks. We find that the fraction of disks three or more
times brighter than the stellar photospheres at 24 {\mu}m decays relatively
slowly initially and then much more rapidly by ~ 10 Myr. However, there is a
continuing component until ~ 35 Myr, probably due primarily to massive clouds
of debris generated in giant impacts during the oligarchic/chaotic growth
phases of terrestrial planets. If the contribution from primordial disks is
excluded, the evolution of the incidence of these oligarchic/chaotic debris
disks can be described empirically by a log-normal function with the peak at 12
- 20 Myr, including ~ 13 % of the original population, and with a post-peak
mean duration of 10 - 20 Myr.Comment: accepted for publication, the Astrophysical Journal (2017
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