Close white dwarf binaries consisting of a white dwarf and an A-, F-, G-, or K-type main-sequence star, henceforth close WD+AFGK binaries, are ideal systems to understand the nature of type Ia ...supernovae progenitors and to test binary evolution models. In this work we identify 775 WD+AFGK candidates from TGAS (The Tycho-Gaia Astrometric Solution) and Gaia Data Release 2 (DR2), a well-defined sample of stars with available parallaxes, and we measure radial velocities (RVs) for 275 of them with the aim of identifying close binaries. The RVs have been measured from high-resolution spectra obtained at the Xinglong 2.16 m Telescope and the San Pedro Mártir 2.12 m Telescope and/or from available LAMOST DR6 (low-resolution) and RAVE DR5 (medium-resolution) spectra. We identify 23 WD+AFGK systems displaying more than 3 RV variation among 151 systems for which the measured values are obtained from different nights. Our WD+AFGK binary sample contains both AFGK dwarfs and giants, with a giant fraction ∼43%. The close binary fractions we determine for the WD+AFGK dwarf and giant samples are 24% and 15%, respectively. We also determine the stellar parameters (i.e., effective temperature, surface gravity, metallicity, mass, and radius) of the AFGK companions with available high-resolution spectra. The stellar parameter distributions of the AFGK companions that are members of close and wide binary candidates do not show statistically significant differences.
We report the discovery of a peculiar L dwarf from the United Kingdom Infrared Deep Sky Survey Large Area Survey, ULAS J222711−004547. The very red infrared photometry (MKO J − K = 2.79 ± 0.06, WISE ...W1−W2 = 0.65 ± 0.05) of ULAS J222711−004547 makes it one of the reddest brown dwarfs discovered so far. We obtained a moderate resolution spectrum of this target using the XSHOOTER spectrograph on the Very Large Telescope, and we classify it as L7pec, confirming its very red nature. Comparison to theoretical models suggests that the object could be a low-gravity L dwarf with a solar or higher than solar metallicity. Nonetheless, the match of such fits to the spectral energy distribution is rather poor, and this and other less red peculiar L dwarfs pose new challenges for the modelling of ultracool atmospheres, especially to the understanding of the effects of condensates and their sensitivity to gravity and metallicity. We determined the proper motion of ULAS J222711−004547 using the data available in the literature, and we find that its kinematics do not suggest membership of any of the known young associations. We show that applying a simple de-reddening curve to its spectrum allows it to resemble the spectra of the L7 spectroscopic standards without any spectral features that distinguish it as a low-metallicity or low-gravity dwarf. Given the negligible interstellar reddening of the field containing our target, we conclude that the reddening of the spectrum is mostly due to an excess of dust in the photosphere of the target. De-reddening the spectrum using extinction curves for different dust species gives surprisingly good results and suggests a characteristic grain size of ∼0.5 μm. We show that by increasing the optical depth, the same extinction curves allow the spectrum of ULAS J222711−004547 to resemble the spectra of unusually blue L dwarfs and even slightly metal-poor L dwarfs. Grains of similar size also yield very good fits when de-reddening other unusually red L dwarfs in the L5-L7.5 range. These results suggest that the diversity in near-infrared colours and spectra seen in late L dwarfs could be due to differences in the optical thickness of the dust cloud deck.
ABSTRACT
Spectroscopic observations of white dwarfs reveal that many of them are polluted by exoplanetary material, whose bulk composition can be uniquely probed this way. We present a spectroscopic ...and photometric analysis of the DA white dwarf WDJ181417.84−735459.83, an object originally identified to have a strong infrared (IR) excess in the 2MASS and WISE catalogues that we confirmed to be intrinsic to the white dwarf, and likely corresponding to the emission of a dusty disc around the star. The finding of Ca, Fe, and Mg absorption lines in two X-SHOOTER spectra of the white dwarf, taken 8 years apart, is further evidence of accretion from a dusty disc. We do not report variability in the absorption lines between these two spectra. Fitting a blackbody model to the IR excess gives a temperature of 910 ± 50 K. We have estimated a total accretion flux from the spectroscopic metal lines of $|\dot{\rm M}| = 1.784 \times 10^{9}\,$g s−1.
ABSTRACT The unprecedented extent of coverage provided by Kepler observations recently revealed outbursts in two hydrogen-atmosphere pulsating white dwarfs (DAVs) that cause hours-long increases in ...the overall mean flux of up to 14%. We have identified two new outbursting pulsating white dwarfs in K2, bringing the total number of known outbursting white dwarfs to four. EPIC 211629697, with = 10,780 140 K and = 7.94 0.08, shows outbursts recurring on average every 5.0 days, increasing the overall flux by up to 15%. EPIC 229227292, with = 11,190 170 K and = 8.02 0.05, has outbursts that recur roughly every 2.4 days with amplitudes up to 9%. We establish that only the coolest pulsating white dwarfs within a small temperature range near the cool, red edge of the DAV instability strip exhibit these outbursts.
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▶ NiMoS with similar dispersion prepared on Al
2O
3, SiO
2–Al
2O
3 and Al
2O
3-Y zeolite. ▶ Tetralin ring opening and cracking is favored on NiMoS/Al
2O
3-Y zeolite. ▶ Support acidity ...also promotes hydrogenation activities. ▶ Electronic effect or alternative reaction pathway over acidic supports are proposed.
Three NiMo sulfided catalysts with the same active phase content and deposited on different supports (alumina, silica–alumina and alumina-Y zeolite) were prepared aiming to obtain bifunctional catalysts with different acidities and good dispersion of the sulfide phase for analyzing the role of the support acidity on the hydrogenation and hydrocracking activities for the conversion of tetralin. Support acidity promotes the ring opening of tetralin, increasing the yields of aromatic compounds among the reaction products of silica–alumina and alumina-Y zeolite supported catalysts. However, these catalysts also presented high activities for both ring opening/cracking and hydrogenation reactions, respectively associated to the support and to sulfided metal phase, as compared to alumina supported one, which presented essentially hydrogenated products. Although the hydrogenation activity of sulfided catalysts can be modified by neighboring acid sites, the complex reaction network for the tetralin conversion, involving series and parallel steps on both acid and hydrogenation sites, has to be taken in account for explaining the present results.
Azo dyes, common in textile wastewater, have high photolytic and chemical stabilities, which make them difficult to be removed using conventional treatments. This study aims to evaluate a combined ...process using heterogeneous photocatalysis, with ZnO/UV or TiO
/UV (0.6 g catalyst L
solution/2-hr UV radiation), and a biological process for textile wastewater treatment. After the proposed treatments, the color and organic matter removals from synthetic wastewater (SW) and industrial wastewater (IW) were evaluated. For SW, the coupled photocatalytic (ZnO/UV or TiO
/UV)-biological system promoted a high extent of color removal (98%) and total organic carbon (TOC) reduction (>80%). Promising results were obtained with IW using combined photocatalytic (TiO
/UV)-biological treatments, reaching 97% and 63% of color and TOC removal, respectively. This process, coupling heterogeneous photocatalysis and a bioprocess, has proved to be a good alternative for the treatment of textile wastewater, not only for color removal but also for dye mineralization purposes. PRACTITIONER POINTS: A combined process using heterogeneous photocatalysis (ZnO/UV or TiO
/UV) and biological process was evaluated for synthetic (SW) and industrial (IW) textile wastewaters treatment. For SW, coupled process promoted high extent of colour and organic matter removals. For IW, promising results were obtained with TiO
/UV-biological treatment (97% of colour and 63% of organic matter removals).
We investigated the prospects for systematic searches of white dwarfs at low Galactic latitudes, using the VLT Survey Telescope H alpha Photometric Survey of the Galactic plane and Bulge (VPHAS+). We ...targeted 17 white dwarf candidates along sightlines of known open clusters, aiming to identify potential cluster members. We confirmed all the 17 white dwarf candidates from blue/optical spectroscopy, and we suggest five of them to be likely cluster members. We estimated progenitor ages and masses for the candidate cluster members, and compare our findings to those for other cluster white dwarfs. A white dwarf in NGC 3532 is the most massive known cluster member (1.13 ...), likely with an oxygen-neon core, for which we estimate an ... progenitor, close to the mass-divide between white dwarf and neutron star progenitors. A cluster member in Ruprecht 131 is a magnetic white dwarf, whose progenitor mass exceeded 2-3 ... We stress that wider searches, and improved cluster distances and ages derived from data of the ESA Gaia mission, will advance the understanding of the mass-loss processes for low- to intermediate-mass stars. (ProQuest: ... denotes formulae/symbols omitted.)
We present a catalogue of 247 photometrically and spectroscopically confirmed fainter classical Be stars (13 ... r ... 16) in the direction of the Perseus Arm of the Milky Way (-1... < b < +4..., ...120... < l < 140...). The catalogue consists of 181 IPHAS-selected new classical Be stars, in addition to 66 objects that we studied in our previous work more closely, and three stars identified as classical Be stars in earlier work. This study more than doubles the number known in the region. Photometry spanning 0.6-5 ...m, spectral types, and interstellar reddenings are given for each object. The spectral types were determined from low-resolution spectra (... 800-2000), to a precision of 1-3 subtypes. The interstellar reddenings are derived from the (r - i) colour, using a method that corrects for circumstellar disc emission. The colour excesses obtained range from E(B - V) = 0.3 up to 1.6 - a distribution that modestly extends the range reported in the literature for Perseus-Arm open clusters. For around half the sample, the reddenings obtained are compatible with measures of the total sightline Galactic extinction. Many of these are likely to lie well beyond the Perseus Arm. (ProQuest: ... denotes formulae/symbols omitted.)
Using the Hubble Space Telescope, we detail the first abundance analysis enabled by far-ultraviolet spectroscopy of a low-mass (≃0.19 M⊙) white dwarf (WD), GALEX J1717+6757, which is in a 5.9-h ...binary with a fainter, more-massive companion. We see absorption from nine metals, including roughly solar abundances of Ca, Fe, Ti, and P. We detect a significantly sub-solar abundance of C, and put upper limits on N and O that are also markedly sub-solar. Updated diffusion calculations indicate that all metals should settle out of the atmosphere of this 14 900 K, log g = 5.67 WD in the absence of radiative forces in less than 20 yr, orders of magnitude faster than the cooling age of hundreds of Myr. We demonstrate that ongoing accretion of rocky material that is often the cause of atmospheric metals in isolated, more massive WDs is unlikely to explain the observed abundances in GALEX J1717+6757. Using new radiative levitation calculations, we determine that radiative forces can counteract diffusion and support many but not all of the elements present in the atmosphere of this WD; radiative levitation cannot, on its own, explain all of the observed abundance patterns, and additional mechanisms such as rotational mixing may be required. Finally, we detect both primary and secondary eclipses using ULTRACAM high-speed photometry, which we use to constrain the low-mass WD radius and rotation rate as well as update the ephemeris from the discovery observations of this WD+WD binary.
We report the discovery of 42 white dwarfs in the original Kepler mission field, including nine new confirmed pulsating hydrogen-atmosphere white dwarfs (ZZ Ceti stars). Guided by the Kepler-Isaac ...Newton Telescope Survey, we selected white dwarf candidates on the basis of their U − g, g − r, and r − Hα photometric colours. We followed up these candidates with high-signal-to-noise optical spectroscopy from the 4.2-m William Herschel Telescope. Using ground-based, time series photometry, we put our sample of new spectroscopically characterized white dwarfs in the context of the empirical ZZ Ceti instability strip. Prior to our search, only two pulsating white dwarfs had been observed by Kepler. Ultimately, four of our new ZZ Cetis were observed from space. These rich data sets are helping initiate a rapid advancement in the asteroseismic investigation of pulsating white dwarfs, which continues with the extended Kepler mission, K2.
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