813 research outputs found
VLA observations of a sample of galaxies with high far-infrared luminosities
Preliminary results are presented from a radio survey of galaxies detected by the IRAS minisurvey. It was found that the main difference between galaxies selected in the far infrared and those selected in the optical is that the former have higher radio luminosities and that the radio emission is more centrally concentrated. There is some evidence that the strong central radio sources in the galaxies selected in the infrared are due to star formation, the star formation rate divided by the volume in which the star formation is occuring is 100 to 1000 times greater in the galaxies selected in the infrared than in the disks of normal galaxies
HiRes deconvolution of Spitzer infrared images
Spitzer provides unprecedented sensitivity in the infrared (IR), but the spatial resolution is limited by a relatively small aperture (0.85 m) of the primary mirror. In order to maximize the scientific return it is desirable to use processing techniques which make the optimal use of the spatial information in the observations. We have developed a deconvolution technique for Spitzer images. The algorithm, "HiRes" and its implementation has been discussed by Backus et al. in 2005. Here we present examples of Spitzer IR images from the Infrared Array Camera (IRAC) and MIPS, reprocessed using this technique. Examples of HiRes processing include a variety of objects from point sources to complex extended regions. The examples include comparison of Spitzer deconvolved images with high-resolution Keck and Hubble Space Telescope images. HiRes deconvolution improves the visualization of spatial morphology by enhancing resolution (to sub-arcsecond levels in the IRAC bands) and removing the contaminating sidelobes from bright sources. The results thereby represent a significant improvement over previously-published Spitzer images. The benefits of HiRes include (a) sub-arcsec resolution (~0".6-0".8 for IRAC channels); (b) the ability to detect sources below the diffraction-limited confusion level; (c) the ability to separate blended sources, and thereby provide guidance to point-source extraction procedures; (d) an improved ability to show the spatial morphology of resolved sources. We suggest that it is a useful technique to identify features which are interesting enough for follow-up deeper analysis
Predicting the frequencies of diverse exo-planetary systems
Extrasolar planetary systems range from hot Jupiters out to icy comet belts
more distant than Pluto. We explain this diversity in a model where the mass of
solids in the primordial circumstellar disk dictates the outcome. The star
retains measures of the initial heavy-element (metal) abundance that can be
used to map solid masses onto outcomes, and the frequencies of all classes are
correctly predicted. The differing dependences on metallicity for forming
massive planets and low-mass cometary bodies are also explained. By
extrapolation, around two-thirds of stars have enough solids to form Earth-like
planets, and a high rate is supported by the first detections of low-mass
exo-planets.Comment: 5 pages, 2 figures; accepted by MNRA
Kojima-1Lb Is a Mildly Cold Neptune around the Brightest Microlensing Host Star
We report the analysis of additional multiband photometry and spectroscopy and new adaptive optics (AO) imaging of the nearby planetary microlensing event TCP J05074264+2447555 (Kojima-1), which was discovered toward the Galactic anticenter in 2017 (Nucita et al.). We confirm the planetary nature of the light-curve anomaly around the peak while finding no additional planetary feature in this event. We also confirm the presence of apparent blending flux and the absence of significant parallax signal reported in the literature. The AO image reveals no contaminating sources, making it most likely that the blending flux comes from the lens star. The measured multiband lens flux, combined with a constraint from the microlensing model, allows us to narrow down the previously unresolved mass and distance of the lens system. We find that the primary lens is a dwarf on the K/M boundary (0.581 ± 0.033 M⊙) located at 505 ± 47 pc, and the companion (Kojima-1Lb) is a Neptune-mass planet (20.0 ± 2.0 M⊕) with a semimajor axis of 1.08^(+0.62)_(-0.18) au. This orbit is a few times smaller than those of typical microlensing planets and is comparable to the snow-line location at young ages. We calculate that the a priori detection probability of Kojima-1Lb is only ~35%, which may imply that Neptunes are common around the snow line, as recently suggested by the transit and radial velocity techniques. The host star is the brightest among the microlensing planetary systems (K_s = 13.7), offering a great opportunity to spectroscopically characterize this system, even with current facilities
Resolving the terrestrial planet forming regions of HD113766 and HD172555 with MIDI
We present new MIDI interferometric and VISIR spectroscopic observations of
HD113766 and HD172555. Additionally we present VISIR 11um and 18um imaging
observations of HD113766. These sources represent the youngest (16Myr and 12Myr
old respectively) debris disc hosts with emission on <<10AU scales. We find
that the disc of HD113766 is partially resolved on baselines of 42-102m, with
variations in resolution with baseline length consistent with a Gaussian model
for the disc with FWHM of 1.2-1.6AU (9-12mas). This is consistent with the
VISIR observations which place an upper limit of 0."14 (17AU) on the emission,
with no evidence for extended emission at larger distances. For HD172555 the
MIDI observations are consistent with complete resolution of the disc emission
on all baselines of lengths 56-93m, putting the dust at a distance of >1AU
(>35mas). When combined with limits from TReCS imaging the dust at ~10um is
constrained to lie somewhere in the region 1-8AU. Observations at ~18um reveal
extended disc emission which could originate from the outer edge of a broad
disc, the inner parts of which are also detected but not resolved at 10um, or
from a spatially distinct component. These observations provide the most
accurate direct measurements of the location of dust at 1-8AU that might
originate from the collisions expected during terrestrial planet formation.
These observations provide valuable constraints for models of the composition
of discs at this epoch and provide a foundation for future studies to examine
in more detail the morphology of debris discs.Comment: 22 pages, 19 figures, accepted for publication in MNRA
Transience of hot dust around sun-like stars
There is currently debate over whether the dust content of planetary systems
is stochastically regenerated or originates in planetesimal belts evolving in
steady state. In this paper a simple model for the steady state evolution of
debris disks due to collisions is developed and confronted with the properties
of the emerging population of 7 sun-like stars that have hot dust <10AU. The
model shows there is a maximum possible disk mass at a given age, since more
massive primordial disks process their mass faster. The corresponding maximum
dust luminosity is f_max=0.00016r^(7/3)/t_age. The majority (4/7) of the hot
disks exceed this limit by >1000 and so cannot be the products of massive
asteroid belts, rather the following systems must be undergoing transient
events characterized by an unusually high dust content near the star: eta
Corvi, HD69830, HD72905 and BD+20307. It is also shown that the hot dust cannot
originate in a recent collision in an asteroid belt, since there is also a
maximum rate at which collisions of sufficient magnitude to reproduce a given
dust luminosity can occur. Further it is shown that the planetesimal belt
feeding the dust in these systems must be located further from the star than
the dust, typically at >2AU. Other notable properties of the 4 hot dust systems
are: two also have a planetesimal belt at >10AU (eta Corvi and HD72905); one
has 3 Neptune mass planets at <1AU (HD69830); all exhibit strong silicate
features in the mid-IR. We consider the most likely origin for the dust in
these systems to be a dynamical instability which scattered planetesimals
inwards from a more distant planetesimal belt in an event akin to the Late
Heavy Bombardment in our own system, the dust being released from such
planetesimals in collisions and possibly also sublimation.Comment: 16 pages, accepted by ApJ, removed HD128400 as hot dust candidat
Multi-Epoch Observations of HD69830: High Resolution Spectroscopy and Limits to Variability
The main-sequence solar-type star HD69830 has an unusually large amount of
dusty debris orbiting close to three planets found via the radial velocity
technique. In order to explore the dynamical interaction between the dust and
planets, we have performed multi-epoch photometry and spectroscopy of the
system over several orbits of the outer dust. We find no evidence for changes
in either the dust amount or its composition, with upper limits of 5-7% (1
per spectral element) on the variability of the {\it dust spectrum}
over 1 year, 3.3% (1 ) on the broad-band disk emission over 4 years,
and 33% (1 ) on the broad-band disk emission over 24 years. Detailed
modeling of the spectrum of the emitting dust indicates that the dust is
located outside of the orbits of the three planets and has a composition
similar to main-belt, C-type asteroids asteroids in our solar system.
Additionally, we find no evidence for a wide variety of gas species associated
with the dust. Our new higher SNR spectra do not confirm our previously claimed
detection of HO ice leading to a firm conclusion that the debris can be
associated with the break-up of one or more C-type asteroids formed in the dry,
inner regions of the protoplanetary disk of the HD69830 system. The modeling of
the spectral energy distribution and high spatial resolution observations in
the mid-infrared are consistent with a 1 AU location for the emitting
material
A Spitzer IRS Study of Debris Disks Around Planet-Host Stars
Since giant planets scatter planetesimals within a few tidal radii of their
orbits, the locations of existing planetesimal belts indicate regions where
giant planet formation failed in bygone protostellar disks. Infrared
observations of circumstellar dust produced by colliding planetesimals are
therefore powerful probes of the formation histories of known planets. Here we
present new Spitzer IRS spectrophotometry of 111 Solar-type stars, including
105 planet hosts. Our observations reveal 11 debris disks, including two
previously undetected debris disks orbiting HD 108874 and HD 130322. Combining
our 32 micron spectrophotometry with previously published MIPS photometry, we
find that the majority of debris disks around planet hosts have temperatures in
the range 60 < T < 100 K. Assuming a dust temperature T = 70 K, which is
representative of the nine debris disks detected by both IRS and MIPS, we find
that debris rings surrounding Sunlike stars orbit between 15 and 240 AU,
depending on the mean particle size. Our observations imply that the planets
detected by radial-velocity searches formed within 240 AU of their parent
stars. If any of the debris disks studied here have mostly large, blackbody
emitting grains, their companion giant planets must have formed in a narrow
region between the ice line and 15 AU.Comment: Accepted for publication in the Astronomical Journal. 14 pages,
including five figures and two table
Neutral carbon in the Egg Nebula (AFGL 2688)
A search for sub-mm C I emission from seven stars that are surrounded by dense molecular gas shells led to the detection, in the case of the "Egg Nebula' (AFGL 2688), of an 0.9 K line implying a C I/CO value greater than 5. The material surrounding this star must be extremely carbon-rich, and it is suggested that the apparently greater extent of the C I emission region may be due to the effects of the galactic UV field on the shell's chemistry, as suggested by Huggins and Glassgold (1982)
Pathway to the Galactic Distribution of Planets: Combined Spitzer and Ground-Based Microlens Parallax Measurements of 21 Single-Lens Events
We present microlens parallax measurements for 21 (apparently) isolated lenses observed toward the Galactic bulge that were imaged simultaneously from Earth and Spitzer, which was ~1 AU west of Earth in projection. We combine these measurements with a kinematic model of the Galaxy to derive distance estimates for each lens, with error bars that are small compared to the Sun's galactocentric distance. The ensemble therefore yields a well-defined cumulative distribution of lens distances. In principle, it is possible to compare this distribution against a set of planets detected in the same experiment in order to measure the Galactic distribution of planets. Since these Spitzer observations yielded only one planet, this is not yet possible in practice. However, it will become possible as larger samples are accumulated
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