- ID:
- ivo://CDS.VizieR/J/ApJ/750/125
- Title:
- Spitzer imaging of Cepheus OB3b cluster
- Short Name:
- J/ApJ/750/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We map the full extent of a rich massive young cluster in the Cep OB3b association with the Infrared Array Camera and Multi-band Imaging Photometer System instruments aboard the Spitzer Space Telescope and the ACIS instrument aboard the Chandra X-Ray Observatory. At 700 pc, it is revealed to be the second nearest large (>1000 member), young (<5 Myr) cluster known. In contrast to the nearest large cluster, the Orion Nebula Cluster, Cep OB3b is only lightly obscured and is mostly located in a large cavity carved out of the surrounding molecular cloud. Our infrared and X-ray data sets, as well as visible photometry from the literature, are used to take a census of the young stars in Cep OB3b. We find that the young stars within the cluster are concentrated in two sub-clusters; an eastern sub-cluster, near the Cep B molecular clump, and a western sub-cluster, near the Cep F molecular clump. Using our census of young stars, we examine the fraction of young stars with infrared excesses indicative of circumstellar disks. We create a map of the disk fraction throughout the cluster and find that it is spatially variable. Due to these spatial variations, the two sub-clusters exhibit substantially different average disk fractions from each other: 32%+/-4% and 50%+/-6%. We discuss whether the discrepant disk fractions are due to the photodestruction of disks by the high mass members of the cluster or whether they result from differences in the ages of the sub-clusters. We conclude that the discrepant disk fractions are most likely due to differences in the ages.
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- ID:
- ivo://CDS.VizieR/J/ApJ/755/9
- Title:
- Spitzer/IRAC light curves of GJ 436 system
- Short Name:
- J/ApJ/755/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of UCF-1.01, a strong exoplanet candidate with a radius 0.66+/-0.04 times that of Earth (R_{oplus}_). This sub-Earth sized planet transits the nearby M-dwarf star GJ 436 with a period of 1.365862+/-8x10^-6^ days. We also report evidence of a 0.65+/-0.06R_{Earth}_ exoplanet candidate (labeled UCF-1.02) orbiting the same star with an undetermined period. Using the Spitzer Space Telescope, we measure the dimming of light as the planets pass in front of their parent star to assess their sizes and orbital parameters. If confirmed today, UCF-1.01 and UCF-1.02 would be designated GJ 436c and GJ 436d, respectively, and would be part of the first multiple-transiting-planet system outside of the Kepler field. Assuming Earth-like densities of 5.515g/cm3, we predict both candidates to have similar masses (~0.28M_{oplus}_, 2.6 Mars-masses) and surface gravities of ~0.65g (where g is the gravity on Earth). UCF-1.01's equilibrium temperature (T_eq_, where emitted and absorbed radiation balance for an equivalent blackbody) is 860K, making the planet unlikely to harbor life as on Earth. Its weak gravitational field and close proximity to its host star imply that UCF-1.01 is unlikely to have retained its original atmosphere; however, a transient atmosphere is possible if recent impacts or tidal heating were to supply volatiles to the surface. We also present additional observations of GJ 436b during secondary eclipse. The 3.6{mu}m light curve shows indications of stellar activity, making a reliable secondary eclipse measurement impossible. A second non-detection at 4.5{mu}m supports our previous work in which we find a methane-deficient and carbon monoxide-rich dayside atmosphere.
- ID:
- ivo://CDS.VizieR/J/ApJ/660/1532
- Title:
- Spitzer/IRAC-MIPS survey of NGC 2244
- Short Name:
- J/ApJ/660/1532
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a survey of NGC 2244 from 3.6 to 24um with the Spitzer Space Telescope. The 24um-8um-3.6um color composite image of the region shows that the central cavity surrounding the multiple O and B stars of NGC 2244 contains a large amount of cool dust visible only at 24um. Our survey gives a detailed look at disk survivability within the hot-star-dominated environment in this cavity. Using mid-infrared two-color diagrams ([3.6]-[4.5] vs. [5.8]-[8.0]), we identified 337 class II and 25 class I objects out of 1084 objects detected in all four of these bands with photometric uncertainty better than 10%. Including the 24um data, we found 213 class II and 20 class I sources out of 279 stars also detected at this latter band. The center of the class II density contours is in very good agreement with the center of the cluster detected in the 2MASS images. We studied the distribution of the class II sources relative to the O stars and found that the effect of high-mass stars on the circumstellar disks is significant only in their immediate vicinity.
- ID:
- ivo://CDS.VizieR/J/ApJ/832/58
- Title:
- Spitzer/IRAC monitoring of WISE J085510.83-071442.5
- Short Name:
- J/ApJ/832/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Because WISE J085510.83-071442.5 (hereafter WISE 0855-0714) is the coldest known brown dwarf (~250K) and one of the Sun's closest neighbors (2.2pc), it offers a unique opportunity to study a planet-like atmosphere in an unexplored regime of temperature. To detect and characterize inhomogeneities in its atmosphere (e.g., patchy clouds, hot spots), we have performed time-series photometric monitoring of WISE 0855-0714 at 3.6 and 4.5{mu}m with the Spitzer Space Telescope during two 23hr periods that were separated by several months. For both bands, we have detected variability with peak-to-peak amplitudes of 4%-5% and 3%-4% in the first and second epochs, respectively. The light curves are semiperiodic in the first epoch for both bands, but they are more irregular in the second epoch. Models of patchy clouds have predicted a large increase in mid-infrared (mid-IR) variability amplitudes (for a given cloud covering fraction) with the appearance of water ice clouds at T_eff_<375K, so if such clouds are responsible for the variability of WISE 0855-0714, then its small amplitudes of variability indicate a very small deviation in cloud coverage between hemispheres. Alternatively, the similarity in mid-IR variability amplitudes between WISE 0855-0714 and somewhat warmer T and Y dwarfs may suggest that they share a common origin for their variability (i.e., not water clouds). In addition to our variability data, we have examined other constraints on the presence of water ice clouds in the atmosphere of WISE 0855-0714, including the recent mid-IR spectrum from Skemer+ (2016ApJ...826L..17S). We find that robust evidence of such clouds is not yet available.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/80
- Title:
- Spitzer/IRAC observations of five deep fields
- Short Name:
- J/ApJ/769/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Spitzer Extended Deep Survey (SEDS) is a very deep infrared survey within five well-known extragalactic science fields: the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, COSMOS, the Hubble Deep Field North, and the Extended Groth Strip. SEDS covers a total area of 1.46deg^2^ to a depth of 26 AB mag (3{sigma}) in both of the warm Infrared Array Camera (IRAC) bands at 3.6 and 4.5{mu}m. Because of its uniform depth of coverage in so many widely-separated fields, SEDS is subject to roughly 25% smaller errors due to cosmic variance than a single-field survey of the same size. SEDS was designed to detect and characterize galaxies from intermediate to high redshifts (z=2-7) with a built-in means of assessing the impact of cosmic variance on the individual fields. Because the full SEDS depth was accumulated in at least three separate visits to each field, typically with six-month intervals between visits, SEDS also furnishes an opportunity to assess the infrared variability of faint objects. This paper describes the SEDS survey design, processing, and publicly-available data products. Deep IRAC counts for the more than 300000 galaxies detected by SEDS are consistent with models based on known galaxy populations. Discrete IRAC sources contribute 5.6+/-1.0 and 4.4+/-0.8nW/m2/sr at 3.6 and 4.5{mu}m to the diffuse cosmic infrared background (CIB). IRAC sources cannot contribute more than half of the total CIB flux estimated from DIRBE data. Barring an unexpected error in the DIRBE flux estimates, half the CIB flux must therefore come from a diffuse component.
- ID:
- ivo://CDS.VizieR/J/ApJ/816/49
- Title:
- Spitzer/IRAC observations of SMC Cepheids
- Short Name:
- J/ApJ/816/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using Spitzer observations of classical Cepheids we have measured the true average distance modulus of the Small Magellanic Cloud (SMC) to be 18.96+/-0.01_stat_+/-0.03_sys_mag (corresponding to 62+/-0.3kpc), which is 0.48+/-0.01mag more distant than the LMC. This is in agreement with previous results from Cepheid observations, as well as with measurements from other indicators such as RR Lyrae stars and the tip of the red giant branch. Utilizing the properties of the mid-infrared Leavitt Law we measured precise distances to individual Cepheids in the SMC, and have confirmed that the galaxy is tilted and elongated such that its eastern side is up to 20kpc closer than its western side. This is in agreement with the results from red clump stars and dynamical simulations of the Magellanic Clouds and Stream.
- ID:
- ivo://CDS.VizieR/J/ApJ/898/21
- Title:
- Spitzer/IRAC obs. of HD113766 & HD172555 systems
- Short Name:
- J/ApJ/898/21
- Date:
- 21 Mar 2022 07:07:57
- Publisher:
- CDS
- Description:
- We present multiepoch infrared photometry and spectroscopy obtained with warm Spitzer, Subaru, and the Stratospheric Observatory for Infrared Astronomy to assess variability for the young (~20Myr) and dusty debris systems around HD 172555 and HD 113766A. No variations (within 0.5%) were found for the former at either 3.6 or 4.5{mu}m, while significant nonperiodic variations (peak to peak of ~10%-15% relative to the primary star) were detected for the latter. Relative to the Spitzer Infrared Spectrograph spectra taken in 2004, multiepoch mid-infrared spectra reveal no change in either the shape of the prominent 10{mu}m solid-state features or the overall flux levels (no more than 20%) for both systems, corroborating the fact that the population of submicron-size grains that produce the pronounced solid-state features is stable over a decadal timescale. We suggest that these submicron-size grains were initially generated in an optically thick clump of debris of millimeter-size vapor condensates resulting from a recent violent impact between large asteroidal or planetary bodies. Because of the shielding from the stellar photons provided by this clump, intense collisions led to an overproduction of fine grains that would otherwise be ejected from the system by radiation pressure. As the clump is sheared by its orbital motion and becomes optically thin, a population of very fine grains could remain in stable orbits until Poynting-Robertson drag slowly spirals them into the star. We further suggest that the 3-5{mu}m disk variation around HD 113766A is consistent with a clump/arc of such fine grains on a modestly eccentric orbit in its terrestrial zone.
- ID:
- ivo://CDS.VizieR/J/ApJ/759/146
- Title:
- Spitzer/IRAC photometry for 37 Galactic Cepheids
- Short Name:
- J/ApJ/759/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Carnegie Hubble Program (CHP) is designed to calibrate the extragalactic distance scale using data from the post-cryogenic era of the Spitzer Space Telescope. The ultimate goal of the CHP is a systematic improvement in the distance scale leading to a determination of the Hubble constant to within an accuracy of 2%. This paper focuses on the measurement and calibration of the Galactic Cepheid period-luminosity (PL, Leavitt) relation using the warm Spitzer/IRAC 1 and 2 bands at 3.6 and 4.5{mu}m. We present photometric measurements covering the period range 4-70 days for 37 Galactic Cepheids. Data at 24 phase points were collected for each star. Three PL relations of the form M=a(log(P)-1)+b are derived. The method adopted here takes the slope a to be -3.31, as determined from the Spitzer Large Magellanic Cloud (LMC) data of Scowcroft et al. (Cat. J/ApJ/743/76). Using the geometric Hubble Space Telescope guide-star distances to 10 Galactic Cepheids, we find a calibrated 3.6{mu}m PL zero point of -5.80+/-0.03. Together with our value for the LMC zero point, we determine a reddening-corrected distance modulus of 18.48+/-0.04mag to the LMC. The mid-IR period-color diagram and the [3.6]-[4.5] color variation with phase are interpreted in terms of CO absorption at 4.5{mu}m. This situation compromises the use of the 4.5{mu}m data for distance determinations.
- ID:
- ivo://CDS.VizieR/J/ApJ/767/147
- Title:
- Spitzer-IRAC photometry of jets in Vela-D
- Short Name:
- J/ApJ/767/147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of H_2_ jets from young protostars in the Vela-D molecular cloud (VMR-D), based on Spitzer-IRAC data between 3.6 {mu}m and 8.0 {mu}m. Our search has led to the identification of 15 jets (two new discoveries) and about 70 well-aligned knots within 1.2 deg^2^. We compare the Infrared Array Camera (IRAC) maps with observations of the H_2_ 1-0 S(1) line at 2.12 {mu}m, with a Spitzer-MIPS map at 24 {mu}m and 70 {mu}m, and with a map of the dust continuum emission at 1.2 mm. From such a comparison, we find a tight association between molecular jets and dust peaks. The jet candidate exciting sources have been searched for in the published catalog of the young stellar objects of VMR-D. In particular, we searched for all the sources of Class II or (preferentially) earlier which are located close to the jet center and aligned with it. Furthermore, the association between jet and exciting source was validated by estimating the differential extinction between the jet opposite lobes. We are able to find a best-candidate exciting source in all but two jets, for which two alternative candidates are given. Four exciting sources are not (or very barely) observed at wavelengths shorter than 24 {mu}m, suggesting that they are very young protostars. Three of them are also associated with the most compact jets (projected length<~0.1 pc). The exciting source spectral energy distributions (SEDs) have been constructed and modeled by means of all the available photometric data between 1.2 {mu}m and 1.2 mm. From SEDs fits, we derive the main source parameters, which indicate that most of them are low-mass protostars. A significant correlation is found between the projected jet length and the [24]-[70] color, which is consistent with an evolutionary scenario according to which shorter jets are associated with younger sources. A rough correlation is found between IRAC line cooling and exciting source bolometric luminosity, in agreement with the previous literature. The emerging trend suggests that mass loss and mass accretion are tightly related phenomena and that both decrease with time.
- ID:
- ivo://CDS.VizieR/J/AJ/161/177
- Title:
- Spitzer IRAC photometry of 36 JWST calibration stars
- Short Name:
- J/AJ/161/177
- Date:
- 20 Jan 2022
- Publisher:
- CDS
- Description:
- We present infrared photometry of all 36 potential JWST calibrators for which there is archival Spitzer IRAC data. This photometry can then be used to inform the stellar models necessary to provide absolute calibration for all JWST instruments. We describe in detail the steps necessary to measure IRAC photometry from archive retrieval to photometric corrections. To validate our photometry, we examine the distribution of uncertainties from all detections in all four IRAC channels as well as compare the photometry and its uncertainties to those from models, ALLWISE, and the literature. Seventy-five percent of our detections have standard deviations per star of all observations within each channel of less than 3%. The median standard deviations are 1.2%, 1.3%, 1.1%, and 1.9% in 3.6-8.0, respectively. We find less than 8% standard deviations in differences of our photometry with ALLWISE and excellent agreement with literature values (less than 3% difference), lending credence to our measured fluxes. JWST is poised to do groundbreaking science, and accurate calibration and cross-calibration with other missions will be part of the underpinnings of that science.
