Dust Around R Coronae Borealis Stars. I. Spitzer/Infrared Spectrograph Observations

Spitzer/infrared spectrograph (IRS) spectra from 5 to 37 mu m for a complete sample of 31 R Coronae Borealis stars (RCBs) are presented. These spectra are combined with optical and near-infrared photometry of each RCB at maximum light to compile a spectral energy distribution (SED). The SEDs are fitted with blackbody flux distributions and estimates are made of the ratio of the infrared flux from circumstellar dust to the flux emitted by the star. Comparisons for 29 of the 31 stars are made with the Infrared Astronomical Satellite (IRAS) fluxes from three decades earlier: Spitzer and IRAS fluxes at 12 mu m and 25 mu m are essentially equal for all but a minority of the sample. For this minority, the IRAS to Spitzer flux ratio exceeds a factor of three. The outliers are suggested to be stars where formation of a dust cloud or dust puff is a rare event. A single puff ejected prior to the IRAS observations may have been reobserved by Spitzer as a cooler puff at a greater distance from the RCB. RCBs which experience more frequent optical declines have, in general, a circumstellar environment containing puffs subtending a larger solid angle at the star and a quasi-constant infrared flux. Yet, the estimated subtended solid angles and the blackbody temperatures of the dust show a systematic evolution to lower solid angles and cooler temperatures in the interval between IRAS and Spitzer. Dust emission by these RCBs and those in the LMC is similar in terms of total 24 mu m luminosity and [8.0]-[24.0] color index.Spanish Ministry of Science and Innovation (MICINN) AYA-2007-64748NASA GO 50212, 1407Robert A. Welch Foundation of Houston, Texas F-634McDonald Observator

High-Resolution Optical Spectroscopy of DY Cen: Diffuse Interstellar Bands in a Proto-Fullerene Circumstellar Environment?

We search high-resolution and high-quality VLT/UVES optical spectra of the hot R Coronae Borealis star DY Cen for electronic transitions of the C-60 molecule and diffuse interstellar bands (DIBs). We report the non-detection of the strongest C-60 electronic transitions (e. g., those at similar to 3760, 3980, and 4024 angstrom). The absence of C-60 absorption bands may support recent laboratory results, which show that the similar to 7.0, 8.5, 17.4, and 18.8 mu m emission features seen in DY Cen-and other similar objects with polycyclic-aromatic-hydrocarbon-like dominated IR spectra-are attributable to proto-fullerenes or fullerene precursors rather than to C-60. DIBs toward DY Cen are normal for its reddening; the only exception is the DIB at 6284 angstrom (possibly also the 7223 angstrom DIB) which is found to be unusually strong. We also report the detection of a new broad (FWHM similar to 2 angstrom) and unidentified feature centered at similar to 4000 angstrom. We suggest that this new band may be related to the circumstellar proto-fullerenes seen at infrared wavelengths.Director's Discretionary Time (DDT) program 284.D-5048Spanish Ministry of Economy and Competitiveness AYA-2011-27754Robert A. Welch Foundation of Houston, Texas F-634McDonald Observator

A search for diffuse bands in fullerene planetary nebulae: evidence of diffuse circumstellar bands

Large fullerenes and fullerene-based molecules have been proposed as carriers of diffuse interstellar bands (DIBs). The recent detection of the most common fullerenes (C60 and C70) around some planetary nebulae (PNe) now enable us to study the DIBs towards fullerene-rich space environments. We search DIBs in the optical spectra towards three fullerene-containing PNe (Tc 1, M 1-20, and IC 418). Special attention is given to DIBs which are found to be unusually intense towards these fullerene sources. In particular, an unusually strong 4428A absorption feature is a common charateristic of fullerene PNe. Similar to Tc 1, the strongest optical bands of neutral C60 are not detected towards IC 418. Our high-quality (S/N > 300) spectra for PN Tc 1, together with its large radial velocity, permit us to search for the presence of diffuse bands of circumstellar origin, which we refer to as diffuse circumstellar bands (DCBs). We report the first tentative detection of two DCBs at 4428 and 5780 A in the fullerene-rich circumstellar environment around the PN Tc 1. Laboratory and theoretical studies of fullerenes in their multifarious manifestations (carbon onions, fullerene clusters, or even complex species formed by fullerenes and other molecules like PAHs or metals) may help solve the mystery of some of the diffuse band carriers.Comment: Accepted for publication in Astronomy & Astrophysics (16 pages, 10 figures, and 7 Tables); final version (changes regarding PN M 1-20 and language corrected

The Hot R Coronae Borealis Star DY Centauri is a Binary

The remarkable hot R Coronae Borealis (RCB) star DY Cen is revealed to be the first and only binary system to be found among the RCB stars and their likely relatives, including the extreme helium stars and the hydrogen-deficient carbon stars. Radial velocity determinations from 1982 to 2010 have shown that DY Cen is a single-lined spectroscopic binary in an eccentric orbit with a period of 39.67 days. It is also one of the hottest and most H-rich member of the class of RCB stars. The system may have evolved from a common envelope to its current form.Spanish Ministry of Economy and Competitiveness AYA-2011-27754McDonald Observator

Are C60 molecules detectable in circumstellar shells of R Coronae Borealis stars?

The hydrogen-poor, helium-rich and carbon-rich character of the gas around R Coronae Borealis (RCB) stars has been suggested to be a site for formation of C60 molecules. This suggestion is not supported by observations reported here showing that infrared transitions of C60 are not seen in a large sample of RCB stars observed with the Infrared Spectrograph on the Spitzer Space Telescope. The infrared C60 transitions are seen, however, in emission and blended with PAH-features in spectra of DY Cen and possibly also of V854 Cen, the two least hydrogen-deficient (hydrogen deficiency of only ~10-100) RCB stars. The speculation is offered that C60 (and the PAHs) in the moderately H-deficient circumstellar envelopes may be formed by the decomposition of hydrogenated amorphous carbon but fullerene formation is inefficient in the highly H-deficient environments of most RCBs.Comment: accepted for publication in The Astrophysical Journal (12 pages, 1 table and 4 figures

The relationship between sleep quality and all-cause, CVD and cancer mortality: the Southall and Brent REvisited study (SABRE)

Background: Both long and short sleep duration increase risk of mortality. Most previous studies have been performed in Europeans and have focused on sleep duration. Thus, we aimed to investigate the association between sleep quality and mortality across three different ethnic groups. / Methods: We used data from the Southall and Brent REvisited Study (SABRE) cohort, which comprises first generation migrant South Asian and African Caribbean men and women, aged 40–69 years, recruited between 1988 and 1991. In sum, 4399 participants provided complete data at baseline and follow-up. Of those, 1656 died by December 2017. Our exposures (eg, difficulty falling asleep, early morning waking and waking up tired in the morning) were self-reported and our primary outcome was mortality. We used Cox proportional hazards models to analyse our data, adjusting for baseline-measured confounders. / Results: None of the sleep measures were strongly associated with all-cause mortality in Europeans or African Caribbeans, whilst in South Asians difficulty falling asleep was related to an increased risk of all-cause mortality (HR = 1.28, 95%CI = 1.01; 1.61). In Europeans, early morning waking was associated with a moderately increased risk of cardiovascular death (HR = 1.31, 95%CI = 1.05; 1.63); alternately, this association was not as strong in the other groups. / Conclusion: Our findings suggest that the relationship between sleep quality and mortality may differ by ethnic group, but formal heterogeneity tests indicated that the strongest difference in HRs was observed for early morning waking and cardiovascular disease (CVD) mortality across the three groups (Cochran's Q test p = 0.036). As such, these results are novel and provide support for ethnic differences in sleep quality and mortality, and may have implications for precision medicine