(ABRIDGED) Studies of debris disks have shown that most systems are analogous to the Edgeworth-Kuiper Belt. However a rare subset of sun-like stars possess dust which lies in the terrestrial planet region. In this study we aim to determine how many sources with apparent mid-IR excess are truly hosts of warm dust, and investigate where the dust must lie. We observed using mid-IR imaging with TIMMI2, VISIR and MICHELLE a sample of FGK main sequence stars reported to have hot dust. A new modelling approach was developed to determine the constraints that can be set on the radial extent of excess emission. We confirm the presence of warm dust around 3 of the candidates (eta Corvi, HD145263 and HD202406), and present constraints on the emitting dust regions. Of 2 alternative models for the eta Corvi excess emission, we find that a model with 1 hot dust component at <3 AU (combined with the known submm dust population) fits the data better at the 2.6sigma level than an alternative model with 2 populations of dust in the mid-IR. We identify several systems which have a companion (HD65277 and HD79873) or background object (HD53246, HD123356 and HD128400) responsible for their mid-infrared excess, and for 3 other systems we were able to rule out a point-like source near the star at the level of excess observed in lower resolution observations (HD12039, HD69830 and HD191089). Hot dust sources are either young and possibly primordial or transitional, or have relatively small radius steady-state planetesimal belts, or they are old and luminous with transient emission. High resolution imaging can be used to constrain the location of the disk and help to discriminate between different models of disk emission. For some small disks, interferometry is needed to resolve the disk location.
Using photometric data from the 2MASS and GLIMPSE catalogues, I investigate the incidence of mid-infrared excesses (~10 microns) of G and K stars of luminosity class III. In order to obtain a large sample size, stars are selected using a near-IR colour-magnitude diagram. Sources which are candidates for showing mid-IR excess are carefully examined and modelled to determined whether they are likely to be G/K giants. It is found that mid-IR excesses are present at a level of (1.8 +/- 0.4) x 10^-3. While the origin of these excesses remains uncertain, it is plausible that they arise from debris d…
Hydrogen atmosphere white dwarfs with metals, so-called DAZs, require external accretion of material to explain the presence of weak metal line absorption in their photospheres. The source of this material is currently uknown, but could come from the interstellar medium, unseen companions, or relic planetesimals from asteroid belt or Kuiper belt analogues. Mid-infrared photometry of these white dwarfs provide additional information to solve the mystery of this accretion and to look for evidence of planetary systems that have survived post main sequence evolution. We present {\em Spitzer} IRAC …
Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, require external accretion of material to explain the presence of weak metal line absorption in their photospheres. The source of this material is currently unknown, but could come from the interstellar medium, unseen companions, or relic planetesimals from asteroid belt or Kuiper belt analogues. Accurate mid-infrared photometry of these white dwarfs provide additional information to solve the mystery of this accretion and to look for evidence of planetary systems that have survived post main sequence evolution. We present {\em…
Spitzer IRAC 3.6-8 micron photometry obtained as part of the GLIMPSE survey has revealed mid-infrared excesses for 33 field stars with known spectral types in a 1.2 sq. degree field centered on the southern Galactic HII region RCW49. These stars comprise a subset of 184 stars with known spectral classification, most of which were pre-selected to have unusually red IR colors. We propose that the mid-IR excesses are caused by circumstellar dust disks that are either very late remnants of stellar formation or debris disks generated by planet formation. Of these 33 stars, 29 appear to be main-sequ…
We investigate the nature of the mid-IR excess for 31 intermediate-mass stars that exhibit an 8 micron excess in either the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire or the Mid-Course Space Experiment using high resolution optical spectra to identify stars surrounded by warm circumstellar dust. From these data we determine projected stellar rotational velocities and estimate stellar effective temperatures for the sample. We estimate stellar ages from these temperatures, parallactic distances, and evolutionary models. Using MIPS [24] measurements and stellar parameters we determi…
We have combined new I, J, H, and Ks imaging of portions of the Chamaeleon II, Lupus I, and Ophiuchus star-forming clouds with 3.6 to 24 micron imaging from the Spitzer Legacy Program, "From Molecular Clouds to Planet Forming Disks", to identify a sample of 19 young stars, brown dwarfs and sub-brown dwarfs showing mid-infrared excess emission. The resulting sample includes sources with luminosities of 0.5>log(L/Lsun)>-3.1. Six of the more luminous sources in our sample have been previously identified by other surveys for young stars and brown dwarfs. Five of the sources in our sample have nomi…
Early observations of T Tauri stars suggested that stars with evidence of circumstellar accretion disks rotated slower than stars without such evidence, but more recent results are not as clear. Near-IR circumstellar disk indicators, though the most widely available, are subject to uncertainties that can result from inner disk holes and/or the system inclination. Mid-infrared observations are less sensitive to such effects, but until now, these observations have been difficult to obtain. The Spitzer Space Telescope now easily enables mid-infrared measurements of large samples of PMS stars cove…
We have identified 230 Tycho-2 Spectral Catalog stars that exhibit 8 micron mid-infrared extraphotospheric excesses in the MidCourse Space Experiment (MSX) and Spitzer Space Telescope Galactic Legacy MidPlane Survey Extraordinaire (GLIMPSE) surveys. Of these, 183 are either OB stars earlier than B8 in which the excess plausibly arises from a thermal bremsstrahlung component or evolved stars in which the excess may be explained by an atmospheric dust component. The remaining 47 stars have spectral classifications B8 or later and appear to be main sequence or late pre-main-sequence objects harbo…
We present IRAC 3.6, 4.5, 5.8 and 8 micron photometry for the 17 A, K and M type members of the Eta Chameleontis association. These data show infrared excesses toward six of the 15 K and M stars, indicating the presence of circumstellar disks around 40% of the stars with masses of 0.1-1 solar mass. The two A-stars show no infrared excesses. The excess emission around one of the stars is comparable to the median excess for classical T Tauri stars in the Taurus association; the remaining five show comparatively weak excess emission. Taking into account published Halpha spectroscopy that shows th…
The mid- to far-infrared emission of the outbursting FU Orionis objects has been attributed either to a flared outer disk or to an infalling envelope. We revisit this issue using detailed radiative transfer calculations to model the recent, high signal-to-noise data from the IRS instrument on the {Spitzer Space Telescope}. In the case of FU Ori, we find that a physically-plausible flared disk irradiated by the central accretion disk matches the observations. Building on our previous work, our accretion disk model with outer disk irradiation by the inner disk reproduces the spectral energy dist…
Observations at 70 microns with the Spitzer Space Telescope have detected several stellar systems within 65 pc of the Sun. Of 18 presumably young systems detected in this study, as many as 15 have 70-micron emission in excess of that expected from their stellar photospheres. Five of the systems with excesses are members of the Tucanae Association. The 70-micron excesses range from a factor of ~2 to nearly 30 times the expected photospheric emission from these stars. In contrast to the 70-micron properties of these systems, there is evidence for an emission excess at 24 microns for only HD 3003…
Mid-infrared (10-25 \micron) imaging of the protostellar binary system L1448N-IRS3(A,B) is presented. Only one source, IRS3(A), was detected at mid-infrared wavelengths -- all of the mid-infrared emission from IRS3(A,B) emanates from IRS3(A). The mid-infrared luminosity of IRS3(A) is $L_{midir} = 1.3(\frac{d}{300\rm{pc}})^2 L_\sun$, which yields a central source mass, depending on the mass infall rate, of $M_* = 0.2 M_\sun \frac{10^{-6}M_\sun yr^{-1}}{\dot M}$. The envelope mass surrounding IRS3(A) is $\sim 0.15 M_\sun$, suggesting that the central source and the envelope are of comparable mas…
We make use of new near and mid-IR photometry of the Pleiades cluster in order to help identify proposed cluster members. We also use the new photometry with previously published photometry to define the single-star main sequence locus at the age of the Pleiades in a variety of color-magnitude planes. The new near and mid-IR photometry extend effectively two magnitudes deeper than the 2MASS All-Sky Point Source catalog, and hence allow us to select a new set of candidate very low mass and sub-stellar mass members of the Pleiades in the central square degree of the cluster. We identify 42 new c…
We have investigated the infrared spectra of all 46 Herbig Ae/Be stars for which spectroscopic data is available in the ISO data archive. Our quantitative analysis of these spectra focusses on the emission bands linked to polycyclic aromatic hydrocarbons (PAHs), the amorphous 10 micron silicate band and the crystalline silicate band at 11.3 micron. We have detected PAH emission in 57% of the Herbig stars in our sample. Clear examples of differences in the PAH spectra are present within our sample, indicating differences in PAH size, chemistry and/or ionization. Amorphous silicate emission was …
We report observations from the Spitzer Space Telescope (SST) regarding the frequency of 24 micron excess emission toward sun-like stars. Our unbiased sample is comprised of 309 stars with masses 0.7-2.2 Msun and ages from <3 Myr to >3 Gyr that lack excess emission at wavelengths <=8 microns. We identify 30 stars that exhibit clear evidence of excess emission from the observed 24/8 micron flux ratio. The implied 24 micron excesses of these candidate debris disk systems range from 13 % (the minimum detectable) to more than 100 % compared to the expected photospheric emission. The frequency of s…
We analyze 8 sources with strong mid-infrared excesses in the 13 Myr-old double cluster h and chi Persei. New optical spectra and broadband SEDs (0.36-8 mu_m) are consistent with cluster membership. We show that material with T ~ 300-400 K and Ld/Lstar ~ 10^-4-10^-3 produces the excesses in these sources. Optically-thick blackbody disk models - including those with large inner holes - do not match the observed SEDs. The SEDs of optically-thin debris disks produced from terrestrial planet formation calculations match the observations well. Thus, some h and chi Persei stars may have debris from …
Fluxes and upper limits in the wavelength range from 3.6 to 70 microns from the Spitzer Space Telescope are provided for twenty solar-mass Pleiades members. One of these stars shows a probable mid-IR excess and two others have possible excesses, presumably due to circumstellar debris disks. For the star with the largest, most secure excess flux at MIPS wavelengths, HII1101, we derive Log(L[dust]/L[Sun]) ~ -3.8 and an estimated debris disk mass of 4.2 x 10^-5 M(Earth) for an assumed uniform dust grain size of 10 microns If the stars with detected excesses are interpreted as stars with relativel…
The incidence of dusty debris disks around low- and intermediate-mass stars has been investigated numerous times in order to understand the early stages of planet formation. Most notably, the IRAS mission observed the entire sky at mid- and far-IR wavelengths, identifying the first debris disk systems, but was unable to detect a statistically significant sample of warm debris disks due to its limited sensitivity at 12 microns. Using Tycho-2 Spectral Catalog stars previously shown to exhibit 8 micron mid-infrared circumstellar excesses confirmed at 24 microns in the Spitzer GLIMPSE survey, we i…
We have surveyed the 30 Myr-old cluster NGC 2547 for planetary debris disks using Spitzer. At 4.5-8 um we are sensitive to the photospheric level down to mid-M stars (0.2 Msol) and at 24 um to early-G stars (1.2 Msol). We find only two to four stars with excesses at 8 um out of ~400-500 cluster members, resulting in an excess fraction <~1 percent at this wavelength. By contrast, the excess fraction at 24 um is ~40 percent (for B-F types). Out of four late-type stars with excesses at 8 um two marginal ones are consistent with asteroid-like debris disks. Among stars with strong 8 um excesses one…
We have conducted deep mid-infrared imaging of a relatively nearby sample of candidate Vega-like stars using the OSCIR instrument on the CTIO 4-meter and Keck II 10-meter telescopes. Our discovery of a spatially-resolved disk around HR 4796A has already been reported (Jayawardhana et al. 1998). Here we present imaging observations of the other members of the sample, including the discovery that only the primary in the HD 35187 binary system appears to harbor a substantial circumstellar disk and the possible detection of extended disk emission around 49 Ceti. We derive global properties of the …
We carried out a search for M-type Vega-like stars by correlating the IRAS Faint Source Catalog with Hipparcos selected M-type stars. Three stars with apparent IRAS 25mu excess emission are shown instead to be non-IR-excess stars from ground-based 11.7 and 17.9mu photometry. Two stars previously suggested to have Vega-like mid-IR excess are also shown to be non-excess stars. These results imply that other suggested mid-IR excess stars in the literature may also be false excess stars. Detection threshold bias is apparently responsible for these bogus IR excesses. Sixty micron excess emission fr…
IZw18, a blue compact dwarf (BCD) galaxy with the 2nd lowest metallicity measured in a star-forming object, has been observed with all three instruments on board the Spitzer Space Telescope. We present the deepest 5-36 micron mid-infrared (mid-IR) spectrum of this galaxy as yet obtained, as well as 3.6 to 70 micron imaging results. As with SBS0335-052E, another BCD with similar metallicity, IZw18 shows no detectable emission from polycyclic aromatic hydrocarbons (PAHs). However, the continuum emission, from 15 to 70 micron, of IZw18 has a much steeper slope, more characteristic of a typical st…
Solar mid-IR observations in the 8-15 micrometer band continuum with moderate angular resolution (18 arcseconds) reveal the presence of bright structures surrounding sunspots. These plage-like features present good association with calcium CaII K1v plages and active region magnetograms. We describe a new optical setup with reflecting mirrors to produce solar images on the focal plane array of uncooled bolometers of a commercial camera preceded by germanium optics. First observations of a sunspot on September 11, 2006 show a mid-IR continuum plage exhibiting spatial distribution closely associa…
We present post-outburst observations of the mid-infrared spectrum and submillimeter continuum of the illuminating source of the newly-discovered McNeil's Nebula in the L1630 region of Orion. The 12 micron flux of this source has increased by a factor of 25 after the outburst, whereas the submillimeter continuum remains at its pre-outburst level. The bolometric luminosity has increased by at least an order of magnitude, to ~34 L_sun, and is likely less than 90 L_sun. The mid-infrared spectrum exhibits a strong and red continuum with no emission or absorption features. The infrared slope of the…
We study the 37 brightest radio sources in the Subaru/XMM-Newton Deep Field (SXDF). Using mid-IR (Spitzer MIPS 24 micron) data we expect to trace nuclear accretion activity, even if it is obscured at optical wavelengths, unless the obscuring column is extreme. Our results suggest that above the `FRI/FRII' radio luminosity break most of the radio sources are associated with objects that have excess mid-IR emission, only some of which are broad-line objects, although there is one clear low-accretion-rate FRI. The fraction of objects with mid-IR excess drops dramatically below the FRI/FRII break,…
We present mid-infrared (10.4 \micron, 11.7 \micron, and 18.3 \micron) imaging intended to locate and characterize the suspected protostellar components within the Bok globule CB54. We detect and confirm the protostellar status for the near-infrared source CB54YC1-II. The mid-infrared luminosity for CB54YC1-II was found to be $L_{midir} \approx 8 L_\sun$, and we estimate a central source mass of $M_* \approx 0.8 M_\sun$ (for a mass accretion rate of ${\dot M}=10^{-6} M_\sun yr^{-1}$). CB54 harbors another near-infrared source (CB54YC1-I), which was not detected by our observations. The non-det…
We present mid-IR photometric properties for a sample of 28 early-type galaxies observed at 6.75, 9.63 and 15 um with the ISOCAM instrument on board the ISO satellite. We find total mid-IR luminosities in the range 3-48x10^8 L_sun. The spectral energy distribution (SED) of the galaxies were derived using the mid-IR data together with previously published UV, optical and near-IR data. These SEDs clearly show a mid-IR emission coming from dust heated at T ~ 260 K. Dust grains properties are inferred from the mid-IR colors. The masses of the hot dust component are in the range 10-400 M_sun. The r…
D Whysong and I have been carrying out a mid-IR survey of 3C radio galaxies to see which have IR-excesses, interpretable as hidden Type-1 AGN. Mostly due to relentless bad weather, we have a modest collections of observations so far. However, we can say with confidence that some radio galaxies are true kinetic, nonthermal emitters, with negligible energetic contributifrom a visible or hidden Big Blue Bump. To make up for the modest collection of mid-IR observations so far, we also present a new spectropolarimetric discovery regarding the underlying shape of the quasar Big Blue Bump in the Balm…
We report spectra obtained with the Spitzer Space Telescope in the wavelength range between 14 microns and 35 microns of 19 nearby main-sequence stars with infrared excesses. The six stars with strong dust emission show no recognizable spectral features, suggesting that the bulk of the emitting particles have diameters larger than 10 microns. If the observed dust results from collisional grinding of larger solids, we infer minimum masses of the parent body population between 0.004 of the Earth's mass and 0.06 of the Earth's mass. We estimate grain production rates of 10 Gg/s around lambda Boo …
We present data obtained with the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope (Spitzer) for a sample of 74 young (t < 30 Myr old) Sun-like (0.7 < M(star)/M(Sun) < 1.5) stars. These are a sub-set of the observations that comprise the Spitzer Legacy science program entitled the Formation and Evolution of Planetary Systems (FEPS). Using IRAC we study the fraction of young stars that exhibit 3.6-8.0 micron infrared emission in excess of that expected from the stellar photosphere, as a function of age from 3-30 Myr. The most straightforward interpretation of such excess emission…
We present mid-IR N-band $(λ_{eff} = 10.2\micron)$ photometry of a carefully selected sample of T Tauri stars thought to be single from the Taurus-Auriga molecular cloud. Infrared excesses in these stars are generally attributed to circumstellar dust-disks. Combining observations at 2.16$\micron$ (K$_{s}$-band) and 10.2$\micron$ (N-band) we probe a region in the circumstellar dust-disk from a few stellar radii through the terrestrial planet zone (0.02-1.0AU). By analyzing the distribution of the $(K_{s}-N)$ color index with respect to previously measured photometric rotation periods we investi…
The metal deficient (Z = Z_sun/41) Blue Compact Dwarf Galaxy (BCD) SBS 0335-052 was observed with ISOCAM between 5 and 17 mic. With a L_12mic/L_B ratio of 2.15, the galaxy is unexpectedly bright in the mid-infrared for such a low-metallicity object. The mid-infrared spectrum shows no sign of the Unidentified Infrared Bands, which we interpret as an effect of the destruction of their carriers by the very high UV energy density in SBS 0335-052. The spectral energy distribution (SED) is dominated by a very strong continuum which makes the ionic lines of [SIV] and [NeIII] very weak. From 5 to 17 m…
(abridged) We present panoramic Spitzer MIPS 24um observations covering 9x9Mpc (25'x25') fields around two massive clusters, Cl0024+16 and MS0451-03, at z=0.39 and z=0.55. Our observations cover a very wide range of environments within these clusters, from high-density regions around the cores out to the turn-around radius. Cross-correlating the mid-infrared catalogs with deep optical and near-infrared imaging of these fields, we investigate the optical/near-infrared colors of the mid-infrared sources. We find excesses of mid-infrared sources with optical/near-infrared colors expected of clust…
We study the mid-infrared properties of a sample of 69 nearby spiral galaxies, selected to avoid Seyfert activity contributing a significant fraction of the central energetics, or strong tidal interaction, and to have normal infrared luminosities. These observations were obtained with ISOCAM, which provides an angular resolution of the order of 10 arcsec (half-power diameter of the point spread function) and low-resolution spectro-imaging information. Between 5 and 18 microns, we mainly observe two dust phases, aromatic infrared bands and very small grains, both out of thermal equilibrium. On …
Results of a comprehensive, new, ground-based mid-infrared imaging survey of the young stellar population of the Rho Ophiuchi cloud are presented. Data were acquired at the Palomar 5-m and at the Keck 10-m telescopes with the MIRLIN and LWS instruments, at 0.25 arcsec and 0.25 arcsec resolutions, respectively. Of 172 survey objects, 85 were detected. Among the 22 multiple systems observed, 15 were resolved and their individual component fluxes determined. A plot of the frequency distribution of the detected objects with SED spectral slope shows that YSOs spend ~400,000 yr in the Flat Spectrum …
We present ground-based mid-infrared imaging for 27 M-, S- and C-type Asymptotic Giant Branch (AGB) stars. The data are compared with those of the database available thanks to the IRAS, ISO, MSX and 2MASS catalogues. Our goal is to establish relations between the IR colors, the effective temperature $T_{eff}$, the luminosity $L$ and the mass loss rate $\dot M$, for improving the effectiveness of AGB modelling. Bolometric (absolute) magnitudes are obtained through distance compilations, and by applying previously-derived bolometric corrections; the variability is also studied, using data accumu…
We study magnetic field steepening due to ambipolar diffusion (Brandenburg & Zweibel 1994) in protoplanetary disk environments and draw the following conclusions. Current sheets are generated in magnetically active regions of the disk where the ionization fraction is high enough for the magnetorotational instability to operate. In late stages of solar nebula evolution, the surface density is expected to have lowered and dust grains to have gravitationally settled to the midplane. If the local dust-to-gas mass ratio near the midplane is increased above cosmic abundances by factors > 10^3, curre…
We present late-time optical and mid-infrared observations of the Type-II supernova 2003gd in NGC 628. Mid-infrared excesses consistent with cooling dust in the ejecta are observed 499-678 days after outburst, and are accompanied by increasing optical extinction and growing asymmetries in the emission-line profiles. Radiative-transfer models show that up to 0.02 solar masses of dust has formed within the ejecta, beginning as early as 250 days after outburst. These observations show that dust formation in supernova ejecta can be efficient and that massive-star supernovae can be major dust produ…
The Hubble Ultra Deep Field source JD2 presented in Mobasher et al. (2005) is an unusual galaxy that is very faint at all wavelengths shortward of 1.1 micron. Photometric redshift fits to data at 0.4 to 8 microns yield a significant probability that it is an extremely massive galaxy at z~6.5. In this paper we present new photometry at 16 microns and 22 micron from Spitzer Infrared Spectrograph (IRS) peak-up imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We find that the spectral energy distribution shows a factor of ~4 rise in flux density between the 16 micron and 22 m…
We study the 37 brightest radio sources in the Subaru/XMM-Newton Deep Field (SXDF). We have spectroscopic redshifts for 24 of 37 objects and photometric redshifts for the remainder, yielding a median redshift z_med for the whole sample of z_med ~= 1.1 and a median radio luminosity close to the `FRI/FRII' luminosity divide. Using mid-IR (Spitzer MIPS 24 um) data we expect to trace nuclear accretion activity, even if it is obscured at optical wavelengths, unless the obscuring column is extreme. Our results suggest that above the FRI/FRII radio luminosity break most of the radio sources are assoc…
Only a few solar-type main sequence stars are known to be orbited by warm dust particles; the most extreme is the G0 field star BD+20 307 that emits ~4% of its energy at mid-infrared wavelengths. We report the identification of a similarly dusty star HD 23514, an F6-type member of the Pleiades cluster. A strong mid-IR silicate emission feature indicates the presence of small warm dust particles, but with the primary flux density peak at the non-standard wavelength of ~9 micron. The existence of so much dust within an AU or so of these stars is not easily accounted for given the very brief life…
The young eruptive star V1647 Ori was observed with MIDI, the mid-infrared interferometric instrument at the Very Large Telescope Interferometer (VLTI), on March 2, 2005. We present the first spectrally resolved interferometric visibility points for this object. Our results show that (1) the mid-infrared emitting region is extended, having a size of ~ 7 AU at 10 um; (2) no signatures of a close companion can be seen; (3) the 8-13 um spectrum exhibits no obvious spectral features. Comparison with similar observations of Herbig Ae stars suggests that V1647 Ori probably possesses a disk of modera…
Low spectral resolution (delta lambda/lambda ~ 50) mid-infrared observations with high angular resolution (0.3--0.5'') using the Long Wavelength Spectrometer on the Keck I Telescope are reported of the nuclei of five highly luminous infrared bright galaxies. Spectra of eight distinct nuclei, ranging in luminosity from 10^11 L_sun to >10^12 L_sun have been obtained. Four of the nuclei show the characteristic PAH emission features, i.e. 11.3 micron emission as well as the 8.6 micron shoulder of the 7.7 micron band. The other nuclei show either weak PAH emission bands or no evidence for these ban…
We present new Spitzer IRS observations of HD164270 (WC9, WR103). A quantitative analysis of the UV, optical, near- and mid-IR spectrum of HD164270 is presented, allowing for line blanketing and wind clumping, revealing T* ~ 48kK, log L/L_sun ~ 4.9, dM/dt ~ 1e-5 M_sun/yr for a volume filling factor of f \~ 0.1. Our models predict that He is partially recombined in the outer stellar wind, such that recent radio-derived mass-loss rates of WC9 stars have been underestimated. We obtain C/He ~ 0.2 and O/He ~ 0.01 by number from optical diagnostics. Mid-IR fine structure lines of [NeII] 12.8 and [SI…
We review the available near- and mid-infrared photometry for white dwarfs obtained from the Two Micron All-Sky Survey (2MASS) and by the Spitzer Space Telescope. Both data sets have recently been used to seek white dwarfs with infrared excesses due to the presence of unresolved companions or circumstellar disks, and also to derive the atmospheric parameters of cool white dwarfs. We first attempt to evaluate the reliability of the 2MASS photometry by comparing it with an independent set of published JHK CIT magnitudes for 160 cool white dwarf stars, and also by comparing the data with the pred…
We present the first spatial clustering measurements of z~1, 24um-selected, star forming galaxies in the Great Observatories Origins Deep Survey (GOODS). The sample under investigation includes 495 objects in GOODS-South and 811 objects in GOODS-North selected down to flux densities of f_24>20 uJy and z_AB<23.5 mag, for which spectroscopic redshifts are available. The median redshift, IR luminosity and star formation rate (SFR) of the samples are z~0.8, L_IR~4.4 x 10^10 L_sun, and SFR~7.6 M_sun/yr, respectively. We measure the projected correlation function w(r_p) on scales of r_p=0.06-10 h^-1…
We present the results of optical and near-IR spectroscopic and near-IR photometric observations of the emission-line stars Hen3-298 and Hen3-303. Strong emission in the H-alpha line is found in both objects. The presence of Fe II and [O I] emission lines in the spectrum of Hen3-298 indicates that it is a B[e] star. The double-peaked CO line profiles, found in the infrared spectrum of Hen3-298, along with the optical line profiles suggest that the star is surrounded by a rotating circumstellar disk. Both objects also show infrared excesses, similar to those of B[e] stars. The radial velocities…
We summarize the main results of a mid-IR photometric survey with ISO for a few nearby embedded clusters. The sensitivity and spatial resolution of ISOCAM provided a wonderful tool for studies of the youngest stellar clusters, which are still deeply embedded in their parent molecular clouds. Mid-IR photometry is found to be extremely efficient in finding all the young stellar objects (YSOs) with IR excesses, i.e. mainly T Tauri stars surrounded by circumstellar disks and also some Class I sources. The spatial distribution of these sources is highly clustered and even sub-clustered, with a tend…
We report deep Sub-Millimeter Array observations of 26 pre-main-sequence (PMS) stars with evolved inner disks. These observations measure the mass of the outer disk (r ~20-100 AU) across every stage of the dissipation of the inner disk (r < 10 AU) as determined by the IR spectral energy distributions (SEDs). We find that only targets with high mid-IR excesses are detected and have disk masses in the 1-5 M_Jup range, while most of our objects remain undetected to sensitivity levels of M_DISK ~0.2-1.5 M_Jup. To put these results in a more general context, we collected publicly available data to …
New moderate-resolution mid-infrared spectroscopy at 10 micron of 27 infrared galaxies is presented. The galaxies have been chosen from three 60 micron selected and one 12 micron selected complete flux-limited catalogs of galaxies; 17 of these sources have L_IR(8--1000 micron) >= 5 times 10^11 L_sun. A high-resolution spectrum of the source Arp 299B1 is also presented. Combining these new results with previously published results, a nearly complete 60 micron selected flux limited subsample, with L_IR(8--1000 micron) >= 1.6 times 10^11 L_sun of 25 galaxies is defined. Within this subsample, it …
We present $B$ and $V$ light curves of a large stellar flare obtained with the Wide Field Camera at the Isaac Newton 2.5-m telescope (La Palma). The source object is a faint ($m_V=21.38$) foreground star in the field of the Andromeda galaxy, with its most probable spectral type being dM4. We provide an estimate of the total flare energy in the optical range and find it to be of the order of $10^{35}$ erg. The cooling phase of the large flare shows three additional weak flare-like events, which we interpret as results of a triggering mechanism also observed on the Sun during large coronal mass …
The zodiacal light is the dominant source of the mid-infrared sky brightness seen from Earth, and exozodiacal light is the dominant emission from planetary and debris systems around other stars. We observed the zodiacal light spectrum with ISOCAM over 5-16 over a wide range of orientations relative to the Sun and the ecliptic. We present theoretical models for a wide range of particle size distributions and compositions. The observed temperature is as expected for large (>10 um radius), low-albedo (< 0.08), rapidly-rotating, grey particles 1 AU from the Sun. In addition to the continuum, we de…
Astronomical observations of flares from analogs of the early Sun have the potential to give critical insights into the high energy irradiation environment of protoplanetary disks. Solar-mass young stellar objects are significantly more X-ray luminous than the typical low-mass T Tauri star. They undergo frequent strong flaring on a several day time scale. Very powerful flares also occur, but on a longer time frame. The hard X-ray spectrum of these stars become even harder during flaring. The X-rays from these sun-like young stellar objects have the potential to ionize circumstellar material ou…
Recently, several groups of young stars in the solar neighborhood have been discovered. Given their proximity, these systems are ideally suited for detailed studies of star and planet formation. Here we report on a group of young stars associated with the bright F8V star HD 199143. At a distance of only 48 pc, this is the closest YSO group containing a classical T Tauri star (HD 358623; K7-M0e). New ground-based mid-infrared data shows that both HD 199143 and HD 358623 have large infrared excesses due to circumstellar disks. A systematic search for new members of this Capricornius association …
We obtained low resolution (R = 100) mid-infrared (8-13 micron wavelengths) spectra of 8 nearby young main sequence stars with the Keck 1 telescope and Long-Wavelength Spectrometer (LWS) to search for 10 micron silicate (Si-O stretch) emission from circumstellar dust. No stars exhibited readily apparent emission: Spectra were then analyzed by least-squares fitting of a template based on a spectrum of Comet Hale-Bopp. Using this technique, we were able to constrain the level of silicate emission to a threshold ten times below what was previously possible from space. We found one star, HD 17925,…
