The Cosmic Origins Spectrograph

Green, James C.; Froning, Cynthia S.; Osterman, Steve; Ebbets, Dennis; Heap, S. R.; Leitherer, Claus; Linsky, Jeffrey L.; Savage, Blair D.; Sembach, Kenneth R.; Shull, J. M.; Siegmund, Oswald H. W.; Snow, Theodore P.; Spencer, J. R.; Stern, S. A.; Stocke, John T.; Welsh, Barry Y.; Béland, S.; Burgh, Eric B.; Danforth, Charles W.; Keeney, Brian A.; McPhate, Jason B.; Penton, Steven V.; Andrews, John P.; Brownsberger, K. R.; Morse, Jon A.; Wilkinson, Erik

doi:10.1088/0004-637x/744/1/60

Cited by 479 publications

(398 citation statements)

References 70 publications

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“…All observations were obtained with the Cosmic Origins Spectrograph (COS, Green et al 2012) using the G130M grating. We adopted a central wavelength of 1291 Å, which covers the wavelength range from 1130 to 1435 Å, with a gap at 1278−1288 Å due to the space between the two detector segments.…”

Section: Sample Selection and Hst Observationsmentioning

confidence: 99%

The frequency of planetary debris around young white dwarfs

Koester

Gänsicke

Farihi

2014

A&A

454

531

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Context. Heavy metals in the atmospheres of white dwarfs are thought in many cases to be accreted from a circumstellar debris disk, which was formed by the tidal disruption of a rocky planetary body within the Roche radius of the star. The abundance analysis of photospheric elements and conclusions about the chemical composition of the accreted matter are a new and promising method of studying the composition of extrasolar planetary systems. However, ground-based searches for metal-polluted white dwarfs that rely primarily on the detection of the Ca ii K line become insensitive at T eff > 15 000 K because this ionization state depopulates.Aims. We present the results of the first unbiased survey for metal pollution among hydrogen-atmosphere (DA type) white dwarfs with cooling ages in the range 20-200 Myr and 17 000 K < T eff < 27 000 K. Methods. The sample was observed with the Cosmic Origins Spectrograph on board the Hubble Space Telescope in the far ultraviolet range between 1130 and 1435 Å. The atmospheric parameters were obtained using these spectra and optical observations from the literature. Element abundances were determined using theoretical models, which include the effects of element stratification due to gravitational settling and radiative levitation. Results. We find 48 of the 85 DA white dwarfs studied, or 56% show traces of heavy elements. In 25 stars (showing only Si and occasionally C), the elements can be explained by radiative levitation alone, although we argue that accretion has very likely occurred recently. The remaining 23 white dwarfs (27%), however, must be currently accreting. Together with previous studies from the ground and adopting bulk Earth abundances for the debris, accretion rates range from a few 10 5 g s −1 to a few 10 8 g s −1 , with no evident trend in cooling age from ≈40 Myr to ≈2 Gyr. Only a single, modest case of metal pollution (Ṁ < 10 6 g s −1 ) is found among ten white dwarfs with T eff > 23 000 K, in excellent agreement with the absence of infrared excess from dust around these warmer stars. The median, main sequence progenitor of our sample corresponds to an A-type star of ≈2 M , and we find 13 of 23 white dwarfs descending from main sequence 2-3 M , late B-and A-type stars to be currently accreting. Only one of 14 targets with M wd > 0.8 M is found to be currently accreting, which suggests a large fraction of these stars result from double-degenerate mergers, and the merger disks do not commonly reform large planetesimals or otherwise pollute the remnant. We reconfirm our previous finding that two 625 Myr Hyades white dwarfs are currently accreting rocky planetary debris. Conclusions. At least 27% of all white dwarfs with cooling ages 20-200 Myr are accreting planetary debris, but that fraction could be as high as ≈50%. At T eff > 23 000 K, the luminosity of white dwarfs is probably sufficient to vaporize circumstellar dust grains, so no stars with strong metal-pollution are found. Planetesimal disruption events should occur in this cooling age and temper...

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Section: Sample Selection and Hst Observationsmentioning

confidence: 99%

The frequency of planetary debris around young white dwarfs

Koester

Gänsicke

Farihi

2014

A&A

454

531

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“…The G160M spectra provide a velocity resolution of v D~17 km s −1 (R = 16,000-21,000) with seven pixels per resolution element, while the G230L spectra provide a resolution of v D~120 km s −1 (R = 2100-3200) (Osterman et al 2011;Green et al 2012).…”

Section: Hst Observationsmentioning

confidence: 99%

Magnetospheric Accretion in Close Pre-Main-Sequence Binaries

Ardila

Jonhs-Krull

Herczeg

et al. 2015

ApJ

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The transfer of matter between a circumbinary disk and a young binary system remains poorly understood, obscuring the interpretation of accretion indicators. To explore the behavior of these indicators in multiple systems, we have performed the first systematic time-domain study of young binaries in the ultraviolet. We obtained far-and near-ultraviolet HST/COS spectra of the young spectroscopic binaries DQ Tau and UZ Tau E. Here we focus on the continuum from 2800 to 3200 Å and on the C IV doublet (λλ1548.19, 1550.77 Å) as accretion diagnostics. Each system was observed over three or four consecutive binary orbits, at phases ∼0, 0.2, 0.5, and 0.7. Those observations are complemented by ground-based U-band measurements. Contrary to model predictions, we do not detect any clear correlation between accretion luminosity and phase. Further, we do not detect any correlation between C IV flux and phase. For both stars the appearance of the C IV line is similar to that of single Classical T Tauri Stars (CTTSs), despite the lack of stable long-lived circumstellar disks. However, unlike the case in single CTTSs, the narrow and broad components of the C IV lines are uncorrelated, and we argue that the narrow component is powered by processes other than accretion, such as flares in the stellar magnetospheres and/or enhanced activity in the upper atmosphere. We find that both stars contribute equally to the narrow component C IV flux in DQ Tau, but the primary dominates the narrow component C IV emission in UZ Tau E. The C IV broad component flux is correlated with other accretion indicators, suggesting an accretion origin. However, the line is blueshifted, which is inconsistent with its origin in an infall flow close to the star. It is possible that the complicated geometry of the region, as well as turbulence in the shock region, are responsible for the blueshifted line profiles.

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“…This study is also very timely since the Cosmic Origins Spectrograph (COS), a high-sensitivity far-ultraviolet spectrograph onboard HST has started to produce many high-quality quasar spectra at z < 1 (Green et al 2012;Savage et al 2012). These COS quasar observations have opened a new tool to study the low-z Lyα forest.…”

Section: Introductionmentioning

confidence: 99%

The evolution of H i and C iv quasar absorption line systems at 1.9 <z< 3.2

Kim

Partl

Carswell

et al. 2013

A&A

104

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We have investigated the distribution and evolution of ∼3100 intergalactic neutral hydrogen (H i) absorbers with H i column densities log N H i = [12.75, 17.0] at 1.9 < z < 3.2, using 18 high resolution, high signal-to-noise quasar spectra obtained from the ESO VLT/UVES archive. We used two sets of Voigt profile fitting analysis, one including all the available high-order Lyman lines to obtain reliable H i column densities of saturated lines, and another using only the Lyα transition. There is no significant difference between the Lyα-only fit and the high-order Lyman fit results. Combining our Lyα-only fit results at 1.7 < z < 3.6 with high-quality literature data, the mean number density at 0 < z < 4 is not well described by a single power law and strongly suggests that its evolution slows down at z ≤ 1.5 at the high and low column density ranges. We also divided our entire H i absorbers at 1.9 < z < 3.2 into two samples, the unenriched forest and the C iv-enriched forest, depending on whether H i lines are associated with C iv at log N C iv ≥ 12.2 within a given velocity range. The entire H i column density distribution function (CDDF) can be described as the combination of these two well-characterised populations which overlap at log N H i ∼ 15. At log N H i ≤ 15, the unenriched forest dominates, showing a similar power-law distribution to the entire forest. The C iv-enriched forest dominates at log N H i ≥ 15, with its distribution function as ∝N ∼−1.45. However, it starts to flatten out at lower N H i , since the enriched forest fraction decreases with decreasing N H i . The deviation from the power law at log N H i = [14, 17] shown in the CDDF for the entire H i sample is a result of combining two different H i populations with a different CDDF shape. The total H i mass density relative to the critical density is Ω H i ∼ 1.6 × 10 −6 h −1 , where the enriched forest accounts for ∼40% of Ω H i .

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The Cosmic Origins Spectrograph

Cited by 479 publications

References 70 publications

The frequency of planetary debris around young white dwarfs

The frequency of planetary debris around young white dwarfs

Magnetospheric Accretion in Close Pre-Main-Sequence Binaries

The evolution of H i and C iv quasar absorption line systems at 1.9 <z< 3.2

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