13 research outputs found
A Spitzer c2d Legacy Survey to Identify and Characterize Disks with Inner Dust Holes
Understanding how disks dissipate is essential to studies of planet
formation. However, identifying exactly how dust and gas dissipates is
complicated due to difficulty in finding objects clearly in the transition of
losing their surrounding material. We use Spitzer IRS spectra to examine 35
photometrically-selected candidate cold disks (disks with large inner dust
holes). The infrared spectra are supplemented with optical spectra to determine
stellar and accretion properties and 1.3mm photometry to measure disk masses.
Based on detailed SED modeling, we identify 15 new cold disks. The remaining 20
objects have IRS spectra that are consistent with disks without holes, disks
that are observed close to edge-on, or stars with background emission. Based on
these results, we determine reliable criteria for identifying disks with inner
holes from Spitzer photometry and examine criteria already in the literature.
Applying these criteria to the c2d surveyed star-forming regions gives a
frequency of such objects of at least 4% and most likely of order 12% of the
YSO population identified by Spitzer.
We also examine the properties of these new cold disks in combination with
cold disks from the literature. Hole sizes in this sample are generally smaller
than for previously discovered disks and reflect a distribution in better
agreement with exoplanet orbit radii. We find correlations between hole size
and both disk and stellar masses. Silicate features, including crystalline
features, are present in the overwhelming majority of the sample although 10
micron feature strength above the continuum declines for holes with radii
larger than ~7 AU. In contrast, PAHs are only detected in 2 out of 15 sources.
Only a quarter of the cold disk sample shows no signs of accretion, making it
unlikely that photoevaporation is the dominant hole forming process in most
cases.Comment: 24 pages, 18 figures and 8 tables. Fixed a typo in Table
C2D Spitzer-IRS spectra of disks around T Tauri stars: I. Silicate emission and grain growth
Infrared ~5--35 um spectra for 40 solar-mass T Tauri stars and 7
intermediate-mass Herbig Ae stars with circumstellar disks were obtained using
the Spitzer Space Telescope as part of the c2d IRS survey. This work
complements prior spectroscopic studies of silicate infrared emission from
disks, which were focused on intermediate-mass stars, with observations of
solar-mass stars limited primarily to the 10 um region. The observed 10 and 20
um silicate feature strengths/shapes are consistent with source-to-source
variations in grain size. A large fraction of the features are weak and flat,
consistent with um-sized grains indicating fast grain growth (from 0.1--1.0 um
in radius). In addition, approximately half of the T Tauri star spectra show
crystalline silicate features near 28 and 33 um indicating significant
processing when compared to interstellar grains. A few sources show large
10-to-20 um ratios and require even larger grains emitting at 20 um than at 10
um. This size difference may arise from the difference in the depth into the
disk probed by the two silicate emission bands in disks where dust settling has
occurred. The 10 um feature strength vs. shape trend is not correlated with age
or Halpha equivalent width, suggesting that some amount of turbulent mixing and
regeneration of small grains is occurring. The strength vs. shape trend is
related to spectral type, however, with M stars showing significantly flatter
10 um features (larger grain sizes) than A/B stars. The connection between
spectral type and grain size is interpreted in terms of the variation in the
silicate emission radius as a function of stellar luminosity, but could also be
indicative of other spectral-type dependent factors (e.g, X-rays, UV radiation,
stellar/disk winds, etc.).Comment: 17 pages, 13 figures, accepted for publication by ApJ, formatted with
emulateapj using revtex4 v4.
The Mid-infrared Instrument for JWST and Its In-flight Performance
The Mid-Infrared Instrument (MIRI) extends the reach of the James Webb Space Telescope (JWST) to 28.5 μm. It provides subarcsecond-resolution imaging, high sensitivity coronagraphy, and spectroscopy at resolutions of λ/Δλ ∼ 100-3500, with the high-resolution mode employing an integral field unit to provide spatial data cubes. The resulting broad suite of capabilities will enable huge advances in studies over this wavelength range. This overview describes the history of acquiring this capability for JWST. It discusses the basic attributes of the instrument optics, the detector arrays, and the cryocooler that keeps everything at approximately 7 K. It gives a short description of the data pipeline and of the instrument performance demonstrated during JWST commissioning. The bottom line is that the telescope and MIRI are both operating to the standards set by pre-launch predictions, and all of the MIRI capabilities are operating at, or even a bit better than, the level that had been expected. The paper is also designed to act as a roadmap to more detailed papers on different aspects of MIRI
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure
A Spitzer c2d Legacy Survey to Identify and Characterize Disks with Inner Dust Holes
International audienceUnderstanding how disks dissipate is essential to studies of planet formation. However, identifying exactly how dust and gas dissipate is complicated due to the difficulty of finding objects that are clearly in the transition phase of losing their surrounding material. We use Spitzer Infrared Spectrograph (IRS) spectra to examine 35 photometrically selected candidate cold disks (disks with large inner dust holes). The infrared spectra are supplemented with optical spectra to determine stellar and accretion properties and 1.3 mm photometry to measure disk masses. Based on detailed spectral energy distribution modeling, we identify 15 new cold disks. The remaining 20 objects have IRS spectra that are consistent with disks without holes, disks that are observed close to edge-on, or stars with background emission. Based on these results, we determine reliable criteria to identify disks with inner holes from Spitzer photometry, and examine criteria already in the literature. Applying these criteria to the c2d surveyed star-forming regions gives a frequency of such objects of at least 4% and most likely of order 12% of the young stellar object population identified by Spitzer. We also examine the properties of these new cold disks in combination with cold disks from the literature. Hole sizes in this sample are generally smaller than in previously discovered disks and reflect a distribution in better agreement with exoplanet orbit radii. We find correlations between hole size and both disk and stellar masses. Silicate features, including crystalline features, are present in the overwhelming majority of the sample, although the 10 mu m feature strength above the continuum declines for holes with radii larger than similar to 7 AU. In contrast, polycyclic aromatic hydrocarbons are only detected in 2 out of 15 sources. Only a quarter of the cold disk sample shows no signs of accretion, making it unlikely that photoevaporation is the dominant hole-forming process in most cases
Evidence-based psychological treatments for mental disorders: Modifiable barriers to access and possible solutions
The prevalence of mental disorders is high and appears to be growing, yet the majority of individuals who meet diagnostic criteria for a mental disorder are not able to access an adequate treatment. While evidence-based psychological treatments (EBPTs) are effective single or adjunctive treatments for mental disorders, there is also evidence that access to these treatments is diminishing. We seek to highlight modifiable barriers to these problems at the patient, therapist, treatment, organization and government-levels of analysis. A range of solutions to each set of contributors is offered and domains for future research are highlighted. In particular, we focus on the need to continue to work toward innovation in treatment development while also solving the difficulties relating to the dissemination of EBPTs. Several relatively new concepts in the field will be discussed (implementation cliff, program drift, voltage drop and deployment treatment development) and we contrast America and England as examples of government-level processes that are in the process of major change with respect to EBPTs. We conclude that there is a need for people in our field to become more knowledgeable about, and get involved in, shaping public policy