333 research outputs found
Cold giant planets evaporated by hot white dwarfs
Atmospheric escape from close-in Neptunes and hot Jupiters around Sun-like stars driven by extreme ultraviolet (EUV) irradiation plays an important role in the evolution of exoplanets and in shaping their ensemble properties. Intermediate and low mass stars are brightest at EUV wavelengths at the very end of their lives, after they have expelled their envelopes and evolved into hot white dwarfs. Yet the effect of the intense EUV irradiation of giant planets orbiting young white dwarfs has not been assessed. We show that the giant planets in the solar system will experience significant hydrodynamic escape caused by the EUV irradiation from the white dwarf left behind by the Sun. A fraction of the evaporated volatiles will be accreted by the solar white dwarf, resulting in detectable photospheric absorption lines. As a large number of the currently known extrasolar giant planets will survive the metamorphosis of their host stars into white dwarfs, observational signatures of accretion from evaporating planetary atmospheres are expected to be common. In fact, one-third of the known hot single white dwarfs show photospheric absorption lines of volatile elements, which we argue are indicative of ongoing accretion from evaporating planets. The fraction of volatile contaminated hot white dwarfs strongly decreases as they cool. We show that accretion from evaporating planetary atmospheres naturally explains this temperature dependence if more than 50% of hot white dwarfs still host giant planets
SDSS J124043.01+671034.68 : the partially burned remnant of a low-mass white dwarf that underwent thermonuclear ignition?
The white dwarf SDSS J124043.01+671034.68 (SDSS J1240+6710) was previously
found to have an oxygen-dominated atmosphere with significant traces of neon,
magnesium, and silicon. A possible origin via a violent late thermal pulse or
binary interactions have been suggested to explain this very unusual
photospheric composition. We report the additional detection of carbon, sodium,
and aluminium in far-ultraviolet and optical follow-up spectroscopy. No
iron-group elements are detected, with tight upper limits on iron, cobalt and
nickel, suggesting that the star underwent partial oxygen burning, but failed
to ignite silicon burning. Modelling the spectral energy distribution and
adopting the distance based on the Gaia parallax, we infer a low white dwarf
mass, M(wd)=0.41+/-0.05Msun. The large space velocity of SDSS J1240+6710,
computed from the Gaia proper motion and its radial velocity, is compatible
with a Galactic rest-frame velocity of ~250km/s in the opposite direction with
respect to the Galactic rotation, strongly supporting a binary origin of this
star. We discuss the properties of SDSS J1240+6710 in the context of the
recently identified survivors of thermonuclear supernovae, the D6 and LP 40-365
stars, and conclude that it is unlikely related to either of those two groups.
We tentatively suggest that SDSS J1240+6710 is the partially burned remnant of
a low-mass white dwarf that underwent a thermonuclear event.Comment: Accepted for publication in MNRA
The class of n-entire operators
We introduce a classification of simple, regular, closed symmetric operators
with deficiency indices (1,1) according to a geometric criterion that extends
the classical notions of entire operators and entire operators in the
generalized sense due to M. G. Krein. We show that these classes of operators
have several distinctive properties, some of them related to the spectra of
their canonical selfadjoint extensions. In particular, we provide necessary and
sufficient conditions on the spectra of two canonical selfadjoint extensions of
an operator for it to belong to one of our classes. Our discussion is based on
some recent results in the theory of de Branges spaces.Comment: 33 pages. Typos corrected. Changes in the wording of Section 2.
References added. Examples added. arXiv admin note: text overlap with
arXiv:1104.476
GW Librae: Still Hot Eight Years Post-Outburst
We report continued Hubble Space Telescope (HST) ultraviolet spectra and
ground-based optical photometry and spectroscopy of GW Librae eight years after
its largest known dwarf nova outburst in 2007. This represents the longest
cooling timescale measured for any dwarf nova. The spectra reveal that the
white dwarf still remains about 3000 K hotter than its quiescent value. Both
ultraviolet and optical light curves show a short period of 364-373 s, similar
to one of the non-radial pulsation periods present for years prior to the
outburst, and with a similar large UV/optical amplitude ratio. A large
modulation at a period of 2 h (also similar to that observed prior to outburst)
is present in the optical data preceding and during the HST observations, but
the satellite observation intervals did not cover the peaks of the optical
modulation so it is not possible to determine its corresponding UV amplitude.
The similarity of the short and long periods to quiescent values implies the
pulsating, fast spinning white dwarf in GW Lib may finally be nearing its
quiescent configuration.Comment: 6 figures, accepted in A
Bioactivity of Argentinean Essential Oils Against Permethrin-Resistant Head Lice, Pediculus humanus capitis
Infestation with the head louse, Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae), is one of the most common parasitic infestation of humans worldwide. Traditionally, the main treatment for control of head lice is chemical control that is based in a wide variety of neurotoxic synthetic insecticides. The repeated overuse of these products has resulted in the selection of resistant populations of head lice. Thus, plant-derived insecticides, such as the essential oils seem to be good viable alternatives as some have low toxicity to mammals and are biodegradable. We determined the insecticidal activity of 25 essential oils belonging to several botanical families present in Argentina against permethrin-resistant head lice. Significant differences in fumigant activity against head lice were found among the essential oils from the native and exotic plant species. The most effective essential oils were Cinnamomum porphyrium, followed by Aloysia citriodora (chemotype 2) and Myrcianthes pseudomato, with KT50 values of 1.12, 3.02 and 4.09; respectively. The results indicate that these essential oils are effective and could be incorporated into pediculicide formulations to control head lice infestations once proper formulation and toxicological tests are performed
Partly burnt runaway stellar remnants from peculiar thermonuclear supernovae
We report the discovery of three stars that, along with the prototype
LP40-365, form a distinct class of chemically peculiar runaway stars that are
the survivors of thermonuclear explosions. Spectroscopy of the four confirmed
LP 40-365 stars finds ONe-dominated atmospheres enriched with remarkably
similar amounts of nuclear ashes of partial O- and Si-burning. Kinematic
evidence is consistent with ejection from a binary supernova progenitor; at
least two stars have rest-frame velocities indicating they are unbound to the
Galaxy. With masses and radii ranging between 0.20-0.28 Msun and 0.16-0.60
Rsun, respectively, we speculate these inflated white dwarfs are the partly
burnt remnants of either peculiar Type Iax or electron-capture supernovae.
Adopting supernova rates from the literature, we estimate that ~20 LP40-365
stars brighter than 19 mag should be detectable within 2 kpc from the Sun at
the end of the Gaia mission. We suggest that as they cool, these stars will
evolve in their spectroscopic appearance, and eventually become peculiar O-rich
white dwarfs. Finally, we stress that the discovery of new LP40-365 stars will
be useful to further constrain their evolution, supplying key boundary
conditions to the modelling of explosion mechanisms, supernova rates, and
nucleosynthetic yields of peculiar thermonuclear explosions.Comment: 22 pages, 14 figures, 6 tables. Accepted for publication on MNRA
GD 424 - A helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal
The photospheric metal pollution of white dwarfs is now well established as the signature of the accretion of planetary debris. However, the origin of the trace hydrogen detected in many white dwarfs with helium atmospheres is still debated. Here, we report the analysis of GD 424: a metal-polluted, helium-atmosphere white dwarf with a large amount of trace hydrogen. We determined the atmospheric parameters using a hybrid analysis that combines the sensitivity of spectroscopy to the atmospheric composition, log(H/He), with that of photometry and astrometry to the effective temperature, Teff, and surface gravity, log g. The resulting white dwarf mass, radius, and cooling age are \mbox{M_{\mathrm{WD}}}=0.77\pm 0.01\, \mbox{\mathrm{M}_{\odot }}, \mbox{R_{\mathrm{WD}}}=0.0109\pm 0.0001\, \mbox{\mathrm{R}_{\odot }}, and τcool = 215 ± 10 Myr, respectively. We identified and measured the abundances of 11 photospheric metals and argue that the accretion event is most likely either in the increasing or in steady state, and that the disrupted planetesimal resembles either CI chondrites or the bulk Earth in terms of its composition. We suggest that the observed 1.33 × 1022 g of trace hydrogen in GD 424 was at least partly acquired through accretion of water-rich planetary debris in an earlier accretion episode
XGAPS: a sub-arcsec cross-match of galactic plane surveys
We present a sub-arcsec cross-match of Gaia Data Release 3 (DR3) against the INT Galactic Plane Surveys (IGAPS) and the United Kingdom Infrared Deep Sky Survey (UKIDSS). The resulting cross-match of Galactic Plane Surveys (XGAPS) provides additional precise photometry (URGO, g, r, i, Hα, J, H, and K) to the Gaia photometry. In building the catalogue, proper motions given in Gaia DR3 are wound back to match the epochs of the IGAPS constituent surveys (INT Photometric HαSurvey of the Northern Galactic Plane, IPHAS, and the UV-Excess Survey of the Northern Galactic Plane, UVEX) and UKIDSS, ensuring high-proper motion objects are appropriately cross-matched. The catalogue contains 33 987 180 sources. The requirement of >3σ parallax detection for every included source means that distances out to 1–1.5 kpc are well covered. In producing XGAPS, we have also trained a Random Forest classifier to discern targets with problematic astrometric solutions. Selection cuts based on the classifier results can be used to clean colour-magnitude and colour–colour diagrams in a controlled and justified manner, as well as producing subsets of astrometrically reliable targets. We provide XGAPS as a 111 column table. Uses of the catalogue include the selection of Galactic targets for multi-object spectroscopic surveys as well as identification of specific Galactic populations
Stellar archaeology with Gaia: the Galactic white dwarf population
Gaia will identify several 1e5 white dwarfs, most of which will be in the
solar neighborhood at distances of a few hundred parsecs. Ground-based optical
follow-up spectroscopy of this sample of stellar remnants is essential to
unlock the enormous scientific potential it holds for our understanding of
stellar evolution, and the Galactic formation history of both stars and
planets.Comment: Summary of a talk at the 'Multi-Object Spectroscopy in the Next
Decade' conference in La Palma, March 2015, to be published in ASP Conference
Series (editors Ian Skillen & Scott Trager
Aging in a Two-Dimensional Ising Model with Dipolar Interactions
Aging in a two-dimensional Ising spin model with both ferromagnetic exchange
and antiferromagnetic dipolar interactions is established and investigated via
Monte Carlo simulations. The behaviour of the autocorrelation function
is analyzed for different values of the temperature, the waiting
time and the quotient , and being the
strength of exchange and dipolar interactions respectively. Different
behaviours are encountered for at low temperatures as is
varied. Our results show that, depending on the value of , the dynamics
of this non-disordered model is consistent either with a slow domain dynamics
characteristic of ferromagnets or with an activated scenario, like that
proposed for spin glasses.Comment: 4 pages, RevTex, 5 postscript figures; acknowledgment added and some
grammatical corrections in caption
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