We present an estimate of the performance that will be achieved during on-orbit operations of the JWST mid-infrared instrument, MIRI. The efficiency of the main imager and spectrometer systems in ...detecting photons from an astronomical target are presented, based on measurements at subsystem and instrument-level testing, with the end-to-end transmission budget discussed in some detail. The brightest target fluxes that can be measured without saturating the detectors are provided. The sensitivity for long-duration observations of faint sources is presented in terms of the target flux required to achieve a signal-to-noise ratio of 10 after a 10,000 s observation. The algorithms used in the sensitivity model are presented, including the understanding gained during testing of the MIRI flight model and flight-like detectors.
Abstract
We report on five years of 3–5
μ
m photometry measurements obtained by warm Spitzer to track the dust debris emission in the terrestrial zone of HD 166191 in combination with simultaneous ...optical data. We show that the debris production in this young (∼10 Myr) system increased significantly in early 2018 and reached a record high level (almost double by mid 2019) by the end of the Spitzer mission (early 2020), suggesting intense collisional activity in its terrestrial zone likely due to either initial assembling of terrestrial planets through giant impacts or dynamical shake-up from unseen planet-mass objects or recent planet migration. This intense activity is further highlighted by detecting a star-size dust clump, passing in front of the star, in the midst of its infrared brightening. We constrain the minimum size and mass of the clump using multiwavelength transit profiles and conclude that the dust clump is most likely created by a large impact involving objects of several hundred kilometers in size with an apparent period of 142 days (i.e., 0.62 au, assuming a circular orbit). The system’s evolutionary state (right after the dispersal of its gas-rich disk) makes it extremely valuable to learn about the process of terrestrial-planet formation and planetary architecture through future observations.
Debris Disks around Sun-like Stars Trilling, D. E; Bryden, G; Beichman, C. A ...
The Astrophysical journal,
02/2008, Letnik:
674, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We have observed nearly 200 FGK stars at 24 and 70 mu m with the Spitzer Space Telescope. We identify excess infrared emission, including a number of cases where the observed flux is more than 10 ...times brighter than the predicted photospheric flux, and interpret these signatures as evidence of debris disks in those systems. We combine this sample of FGK stars with similar published results to produce a sample of more than 350 main sequence AFGKM stars. The incidence of debris disks is 4.2 super(+) sub(-) super(2) sub(1) super(.) sub(.) super(0) sub(1)% at 24 mu m for a sample of 213 Sun-like (FG) stars and 16.4 super(+) sub(2) super(2) sub(.) super(.) sub(9) super(8-)% at 70 mu m for 225 Sun-like (FG) stars. We find that the excess rates for A, F, G, and K stars are statistically indistinguishable, but with a suggestion of decreasing excess rate toward the later spectral types; this may be an age effect. The lack of strong trend among FGK stars of comparable ages is surprising, given the factor of 50 change in stellar luminosity across this spectral range. We also find that the incidence of debris disks declines very slowly beyond ages of 1 billion years.
We present spectroscopy of the supernova remnant Cassiopeia A (Cas A) observed at infrared wavelengths from 10 to 40 mu m with the Spitzer Space Telescope and at millimeter wavelengths in super(12)CO ...and super(13)CO J = 2-1 (230 and 220 GHz) with the Heinrich Hertz Submillimeter Telescope. The IR spectra demonstrate high-velocity features toward a molecular cloud coincident with a region of bright radio continuum emission along the northern shock front of Cas A. The millimeter observations indicate that CO emission is broadened by a factor of two in some clouds toward Cas A, particularly to the south and west. We believe that these features trace interactions between the Cas A shock front and nearby molecular clouds. In addition, some of the molecular clouds that exhibit broadening in CO lie 1'-2' away from the furthest extent of the supernova remnant shock front. We propose that this material may be accelerated by ejecta with velocity significantly larger than the observed free-expansion velocity of the Cas A shock front. These observations may trace cloud interactions with fast-moving outflows such as the bipolar outflow along the southwest to northeast axis of the Cas A supernova remnant, as well as fast-moving knots seen emerging in other directions.
Abstract
We report Spitzer 3.6 and 4.5
μ
m photometry of 11 bright stars relative to Sirius, exploiting the unique optical stability of the Spitzer Space Telescope point-spread function (PSF). ...Spitzer's extremely stable beryllium optics in its isothermal environment enables precise comparisons in the wings of the PSF from heavily saturated stars. These bright stars stand as the primary sample to improve stellar models, and to transfer the absolute flux calibration of bright standard stars to a sample of fainter standards useful for missions like JWST and for large ground-based telescopes. We demonstrate that better than 1% relative photometry can be achieved using the PSF wing technique in the radial range of 20″–100″ for stars that are fainter than Sirius by 8 mag (from outside the saturated core to a large radius where a high signal-to-noise ratio profile can still be obtained). We test our results by (1) comparing the 3.6−4.5 color with that expected between the WISE W1 and W2 bands, (2) comparing with stars where there is accurate
K
S
photometry, and (3) also comparing with relative fluxes obtained with the DIRBE instrument on COBE. These tests confirm that relative photometry is achieved to better than 1%.
ABSTRACT We study the relation of active galactic nuclei (AGNs) to star formation in their host galaxies. Our sample includes 205 Type-1 and 85 Type-2 AGNs, 162 detected with Herschel, from fields ...surrounding 30 galaxy clusters in the Local Cluster Substructure Survey. The sample is identified by optical line widths and ratios after selection to be brighter than 1 mJy at 24 m. We show that Type-2 AGN O iiiλ5007 line fluxes at high z can be contaminated by their host galaxies with typical spectrograph entrance apertures (but our sample is not compromised in this way). We use spectral energy distribution (SED) templates to decompose the galaxy SEDs and estimate star formation rates (SFRs), AGN luminosities, and host galaxy stellar masses (described in an accompanying paper). The AGNs arise from massive black holes ( ) accreting at ∼10% of the Eddington rate and residing in galaxies with stellar mass ; those detected with Herschel have IR luminosity from star formation in the range of . We find that (1) the specific SFRs in the host galaxies are generally consistent with those of normal star-forming (main sequence) galaxies; (2) there is a strong correlation between the luminosities from star formation and the AGN; and (3) the correlation may not result from a causal connection, but could arise because the black hole mass (and hence AGN Eddington luminosity) and star formation are both correlated with the galaxy mass.
Debris Disk Evolution around A Stars Su, K. Y. L; Rieke, G. H; Stansberry, J. A ...
The Astrophysical journal,
12/2006, Letnik:
653, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We report 24 and/or 70 km measurements of 6160 A-type main-sequence stars using the Multiband Imaging Photometer for Spitzer (MIPS). Their ages range from 5 to 850 Myr, based on estimates from the ...literature (cluster or moving group associations) or from the H-R diagram and isochrones. The thermal infrared excess is identified by comparing the deviation (63% and 615% at the 1 s level at 24 and 70 km, respectively) between the measurements and the synthetic Kurucz photospheric predictions. Stars showing excess infrared emission due to strong emission lines or extended nebulosity seen at 24 km are excluded from our sample; therefore, the remaining infrared excesses are likely to arise from circumstellar debris disks. At the 3 s confidence level, the excess rate at 24 and 70 km is 32% and .33% (with an uncertainty of 5%), considerably higher than what has been found for old solar analogs and M dwarfs. Our measurements place constraints on the fractional dust luminosities and temperatures in the disks. We find that older stars tend to have lower fractional dust luminosity than younger ones. While the fractional luminosity from the excess infrared emission follows a general 1/t relationship, the values at a given stellar age vary by at least 2 orders of magnitude. We also find that (1) older stars possess a narrow range of temperature distribution peaking at colder temperatures, and (2) the disk emission at 70 km persists longer than that at 24 km. Both results suggest that the debris disk clearing process is more effective in the inner regions.
We study the X-ray emission of a representative sample of 27 local luminous infrared galaxies (LIRGs). The median IR luminosity of our sample is log LIR/L⊙ = 11.2, therefore the low-luminosity end of ...the LIRG class is well represented. We used new XMM-Newton data as well as Chandra and XMM-Newton archive data. The soft X-ray (0.5–2 keV) emission of most of the galaxies (>80%), including LIRGs hosting a Seyfert 2 nucleus, is dominated by star-formation-related processes. These LIRGs follow the star-formation rate (SFR) versus soft X-ray luminosity correlation observed in local starbursts. We find that ~15% of the non-Seyfert LIRGs (3 out of 20) have an excessively hard X-ray emission relative to that expected from star-formation, which might indicate the presence of an obscured AGN. The rest of the non-Seyfert LIRGs follow the SFR versus hard X-ray (2–10 keV) luminosity correlation of local starbursts. The non-detection of the 6.4 keV Fe Kα emission line in the non-Seyfert LIRGs allows us to put an upper limit on the bolometric luminosity of an obscured AGN, Lbol <1043 erg s-1. That is, if these galaxies were hosting a low-luminosity AGN, its contribution to the total luminosity would be less than 10%. Finally we estimate that the AGN contribution to the total luminosity for our sample of local LIRGs is between 7% and 10%.
We present multiple epochs of near-infrared spectroscopy for a sample of 25 young stars, including T Tauri, Herbig Ae/Be, and FU Ori objects. Using the FSPEC instrument on the Bok 90-inch telescope, ...we obtained K-band spectra of the Brγ transition of hydrogen, with a resolution of ≈3500. Epochs were taken over a span of >1 yr, sampling time-spacings of roughly 1 d, 1 month, and 1 yr. The majority of our targets show Brγ emission, and in some cases these are the first published detections. Time variability is seen in approximately half of the targets showing Brγ emission. We compare the observed variability with expectations for rotationally modulated accretion on to the central stars and time-variable continuum emission or extinction from matter in the inner disc. Our observations are not entirely consistent with models of rotationally modulated magnetospheric accretion. Further monitoring, over a larger number of epochs, will facilitate more quantitative constraints on variability time-scales and amplitudes, and a more conclusive comparison with theoretical models.
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