Evidence for Mass-dependent Circumstellar Disk Evolution in the 5 Myr Old Upper Scorpius OB Association

We present 4.5, 8, and 16 µm photometry from the Spitzer Space Telescope for 204 stars in the Upper Scorpius OB association. The data are used to investigate the frequency and properties of circumstellar disks around stars with masses between ~0.1 and 20 M_☉ at an age of ~5 Myr. We identify 35 stars that have emission at 8 or 16 µm in excess of the, stellar photosphere. The lower mass stars (~0.1–1.2M_☉) appear surrounded by primordial optically thick disks based on, the excess emission characteristics. Starsmoremassive than ~1.8M_☉ have lower fractional excess luminosities suggesting, that the inner ~10 AU of the disk has been largely depleted of primordial material. None of the G and F stars (~1.2–1.8 M_☉) in our sample have an infrared excess at wavelengths ≤16 µm. These results indicate that the mechanisms for, dispersing primordial optically thick disks operate less efficiently, on average, for low-mass stars, and that longer timescales are available for the buildup of planetary systems in the terrestrial zone for stars with masses ≾1 M_☉

Family Home Visitors: Increasing Minority Women’s Access to Health Services

The article describes how service access barriers (language, trust) were addressed at different levels (organization, service provider, community) by involving Family Home Visitors to support Nurse Practitioners in providing pre- and postnatal services to linguis­tic minority women in Ontario. The investigators undertook a secondary analysis of 18 semi-structured interviews with health unit informants, Nurse Practitioners, program us­ers, and community leaders, including Family Home Visitors. Health units facilitated col­laboration between two programs aimed at serving mothers with young children, result­ing in both programs using Family Home Visitors. They enhanced minority women’s trust in Nurse Practitioner services by providing interpretation, outreach and support. Family Home Visitors increased Nurse Practitioners’ community knowledge and insights of the family situation. The findings contribute to our understanding of strategies to overcome language and trust barriers and improve access to programs for isolated women from linguistic minority backgrounds. Family Home Visitors’ role has the potential for being expanded and deserves more system support

Circumstellar Disks in the Orion Nebula Cluster

We combine our previous optical spectroscopic and photometric analysis of ~1600 stars located in the Orion Nebula Cluster (ONC) with our own and published near-infrared photometric surveys of the region in order to investigate the evidence for and properties of circumstellar disks. We use the near-infrared continuum excess as our primary disk diagnostic, although we also study sources with Ca II triplet emission and those designated as "proplyds." The measured near-infrared excess is influenced by (1) the presence or absence of a circumstellar disk, (2) the relative importance of disk accretion and inner disk holes, (3) the relative contrast between photospheric and disk emission, and (4) system inclination. After attempting to understand the effects of these influences, we estimate the frequency of circumstellar disks and discuss the evidence for trends in the disk frequency with stellar mass (over the mass range <0.1–50 M_⊙), stellar age (over the age range <0.1–2 Myr), and projected cluster radius (over the radial range 0–3 pc). We find that the fraction of stars retaining their inner (<0.1 AU) circumstellar disks to the present time is at least 55% and probably no more than 90%, averaged over the entire range in stellar mass and stellar age represented in the ONC and over the entire area of our survey. We find no trend in the disk fraction with stellar age, at least not over the limited age range of the cluster. We find that more massive stars are less likely to have disks, consistent with a scenario in which the evolutionary timescales are more rapid for disks surrounding more massive stars than for disks surrounding less massive stars. We also find that the disk frequency begins to decrease toward the lowest masses, although objects of all masses (including those that appear to be substellar) can have disks. We find that the disk frequency increases toward the cluster center. We then argue, using several lines of evidence, that a large fraction of the disks associated with stars in the ONC are accretion disks. The observed trends with stellar age, stellar mass, and projected cluster radius in the disk frequency may, in fact, be driven primarily by trends in the disk accretion properties. From the magnitude of the near-infrared excess above that expected from pure irradiation disks, we find an accretion disk fraction among the stars identified as having disks of 61%–88%. In addition, approximately 20% of the stars in our optical spectroscopic sample show broad (several hundred km s^(-1) FWHM) Ca II emission lines, which are features often associated with accretion disk/wind phenomena; another 50% of the sample have Ca II lines that (at our spectral resolution) are "filled in," indicating an independently derived accretion disk frequency of ~70%. Finally, we discuss the near-infrared and optical emission-line properties of that portion of our sample identified from Hubble Space Telescope imaging as having a dark silhouette or an externally ionized structure. This sample, proposed in the literature to have accretion disks, appears to be no different in terms of its stellar or circumstellar properties from the rest of the ONC population. The only feature distinguishing these objects from their ONC siblings thus may be their current (but short-lived) proximity to the massive stars near the cluster center

Prediabetes and Diabetes Are Associated With Arterial Stiffness in Older Adults: The ARIC Study

To determine whether prediabetes and diabetes in older adults are associated with arterial stiffness measured in central and peripheral arteries and to examine characteristics that modify these associations

Formation and Evolution of Planetary Systems: Cold Outer Disks Associated with Sun-like stars

We present the discovery of debris systems around three solar mass stars based upon observations performed with the Spitzer Space Telescope as part of a Legacy Science Program, ``the Formation and Evolution of Planetary Systems'' (FEPS). We also confirm the presence of debris around two other stars. All the stars exhibit infrared emission in excess of the expected photospheres in the 70 micron band, but are consistent with photospheric emission at <= 33 micron. This restricts the maximum temperature of debris in equilibrium with the stellar radiation to T < 70 K. We find that these sources are relatively old in the FEPS sample, in the age range 0.7 - 3 Gyr. Based on models of the spectral energy distributions, we suggest that these debris systems represent materials generated by collisions of planetesimal belts. We speculate on the nature of these systems through comparisons to our own Kuiper Belt, and on the likely planet(s) responsible for stirring the system and ultimately releasing dust through collisions. We further report observations of a nearby star HD 13974 (d =11 pc) that is indistinguishable from a bare photosphere at both 24 micron and 70 micron. The observations place strong upper limits on the presence of any cold dust in this nearby system (L_IR/L_* < 10^{-5.2}).Comment: 31 pages, 9 figures, accepted for publication in Ap

Ten-Micron Observations of Nearby Young Stars

(abridged) We present new 10-micron photometry of 21 nearby young stars obtained at the Palomar 5-meter and at the Keck I 10-meter telescopes as part of a program to search for dust in the habitable zone of young stars. Thirteen of the stars are in the F-K spectral type range ("solar analogs"), 4 have B or A spectral types, and 4 have spectral type M. We confirm existing IRAS 12-micron and ground-based 10-micron photometry for 10 of the stars, and present new insight into this spectral regime for the rest. Excess emission at 10 micron is not found in any of the young solar analogs, except for a possible 2.4-sigma detection in the G5V star HD 88638. The G2V star HD 107146, which does not display a 10-micron excess, is identified as a new Vega-like candidate, based on our 10-micron photospheric detection, combined with previously unidentified 60-micron and 100-micron IRAS excesses. Among the early-type stars, a 10-micron excess is detected only in HD 109573A (HR 4796A), confirming prior observations; among the M dwarfs, excesses are confirmed in AA Tau, CD -40 8434, and Hen 3-600A. A previously suggested N band excess in the M3 dwarf CD -33 7795 is shown to be consistent with photospheric emission.Comment: 40 pages, 4 figures, 5 tables. To appear in the January 1, 2004 issue of Ap

Are Debris Disks and Massive Planets Correlated?

Using data from the Spitzer Space Telescope Legacy Science Program ``Formation and Evolution of Planetary Systems'' (FEPS), we have searched for debris disks around 9 FGK stars (2-10 Gyr), known from radial velocity (RV) studies to have one or more massive planets. Only one of the sources, HD 38529, has excess emission above the stellar photosphere; at 70 micron the signal-to-noise ratio in the excess is 4.7 while at wavelengths < 30 micron there is no evidence of excess. The remaining sources show no excesses at any Spitzer wavelengths. Applying survival tests to the FEPS sample and the results for the FGK survey published in Bryden et al. (2006), we do not find a significant correlation between the frequency and properties of debris disks and the presence of close-in planets. We discuss possible reasons for the lack of a correlation.Comment: 24 pages, 3 figures. Accepted to Astrophysical Journa

Formation and Evolution of Planetary Systems (FEPS): Properties of Debris Dust around Solar-type Stars

We present Spitzer photometric (IRAC and MIPS) and spectroscopic (IRS low resolution) observations for 314 stars in the Formation and Evolution of Planetary Systems (FEPS) Legacy program. These data are used to investigate the properties and evolution of circumstellar dust around solar-type stars spanning ages from approximately 3 Myr to 3 Gyr. We identify 46 sources that exhibit excess infrared emission above the stellar photosphere at 24um, and 21 sources with excesses at 70um. Five sources with an infrared excess have characteristics of optically thick primordial disks, while the remaining sources have properties akin to debris systems. The fraction of systems exhibiting a 24um excess greater than 10.2% above the photosphere is 15% for ages < 300 Myr and declines to 2.7% for older ages. The upper envelope to the 70um fractional luminosity appears to decline over a similar age range. The characteristic temperature of the debris inferred from the IRS spectra range between 60 and 180 K, with evidence for the presence of cooler dust to account for the strength of the 70um excess emission. No strong correlation is found between dust temperature and stellar age. Comparison of the observational data with disk models containing a power-law distribution of silicate grains suggest that the typical inner disk radius is > 10 AU. Although the interpretation is not unique, the lack of excess emission shortwards of 16um and the relatively flat distribution of the 24um excess for ages <300~Myr is consistent with steady-state collisional models.Comment: 85 pages, 18 figures, 4 tables; accepted for publication in ApJ

Detection of cool dust around the G2V star HD 107146

We report the detection of dust emission at sub-millimeter wavelengths from HD 107146, a G2V star with an age estimated to lie between 80 and 200 Myr. The emission is resolved at 450um with a size 300 AU x 210 AU. A fit to the spectral energy distribution gives a dust temperature of 51 K and dust mass of 0.10 Earth masses. No excess emission above the photosphere was detected at 18um showing that there is very little warm dust and implying the presence of a large inner hole, at least 31 AU (~ 1'') in radius, around the star. The properties of this star-disk system are compared with similar observations of other systems. We also discuss prospects for future observations that may be able to determine whether the inner hole is maintained by the dynamical effect of an unseen orbiting companion.Comment: accepted by the Astrophysical Journa

The moth : an unusual circumstellar structure associated with HD 61005

We present the discovery of an unusual spatially resolved circumstellar structure associated with the ≈90 Myr, nearby, G dwarf star HD 61005. Observations from the FEPS Spitzer Legacy Science survey reveal thermal emission in excess of expected stellar photospheric levels. Follow-up 0.1" resolution HST NICMOS coronagraphic images reveal scattered starlight ≤7" (~240 AU) from the occulted star (1.1 μm flux density =18 ± 3.3 mJy; and 0.77% ± 0.16% of the starlight). The extremely high near-IR scattering fraction and IR excess luminosity f = L_(IR)/L_* ≈2 × 10^(−3) suggests scattering particle sizes of order a ~<1.1 μm/2π ~ 0.2 μm , comparable to the blowout size (a ≈ 0.3 μm) due to radiation pressure from the star. Dust-scattered starlight is traced inward to an instrumental limit of ~10 AU. The structure exhibits a strong asymmetry about its morphological major axis but is mirror-symmetric about its minor axis