55 research outputs found
SDSS DR7 white dwarf catalog
We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20,407 white dwarf spectra, representing 19,712 stars, and provide atmospheric model fits to 14,120 DA and 1011 DB white dwarf spectra from 12,843 and 923 stars, respectively. These numbers represent more than a factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalogs based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated log g if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.Facultad de Ciencias Astronómicas y Geofísica
Discovery of 74 new bright ZZ Ceti stars in the first three years of TESS
We report the discovery of 74 new pulsating DA white dwarf stars, or ZZ Cetis, from the data obtained by the Transiting Exoplanet Survey Satellite mission, from Sectors 1 to 39, corresponding to the first 3 cycles. This includes objects from the Southern hemisphere (Sectors 1–13 and 27–39) and the Northern hemisphere (Sectors 14–26), observed with 120 s- and 20 s-cadence. Our sample likely includes 13 low-mass and one extremely low-mass white dwarf candidate, considering the mass determinations from fitting Gaia magnitudes and parallax. In addition, we present follow-up time series photometry from ground-based telescopes for 11 objects, which allowed us to detect a larger number of periods. For each object, we analysed the period spectra and performed an asteroseismological analysis, and we estimate the structure parameters of the sample, i.e. stellar mass, effective temperature, and hydrogen envelope mass. We estimate a mean asteroseismological mass of 〈Msis〉 = 0.635 ± 0.015 M⊙, excluding the candidate low or extremely low-mass objects. This value is in agreement with the mean mass using estimates from Gaia data, which is 〈Mphot〉 = 0.631 ± 0.040 M⊙, and with the mean mass of previously known ZZ Cetis of 〈M*〉 = 0.644 ± 0.034 M⊙. Our sample of 74 new bright ZZ Cetis increases the number of known ZZ Cetis by ∼20 per cent
Follow-up of the Neutron Star Bearing Gravitational-wave Candidate Events S190425z and S190426c with MMT and SOAR
On 2019 April 25.346 and 26.640 UT the LIGO and Virgo gravitational wave (GW)
observatories announced the detection of the first candidate events in
Observing Run 3 that contain at least one neutron star. S190425z is a likely
binary neutron star (BNS) merger at Mpc, while S190426c is
possibly the first NS-BH merger ever detected, at Mpc,
although with marginal statistical significance. Here we report our optical
follow-up observations for both events using the MMT 6.5-m telescope, as well
as our spectroscopic follow-up of candidate counterparts (which turned out to
be unrelated) with the 4.1-m SOAR telescope. We compare to publicly reported
searches, explore the overall areal coverage and depth, and evaluate those in
relation to the optical/NIR kilonova emission from the BNS merger GW170817, to
theoretical kilonova models, and to short GRB afterglows. We find that for a
GW170817-like kilonova, the partial volume covered spans up to about 40% for
S190425z and 60% for S190426c. For an on-axis jet typical of short GRBs, the
search effective volume is larger, but such a configuration is expected in at
most a few percent of mergers. We further find that wide-field -ray and
X-ray limits rule out luminous on-axis SGRBs, for a large fraction of the
localization regions, although these searches are not sufficiently deep in the
context of the -ray emission from GW170817 or off-axis SGRB afterglows.
The results indicate that some optical follow-up searches are sufficiently deep
for counterpart identification to about 300 Mpc, but that localizations better
than 1000 deg are likely essential.Comment: The first six authors contributed equally to this wor
TIC 378898110: A Bright, Short-Period AM CVn Binary in TESS
AM CVn-type systems are ultracompact, helium-accreting binary systems which
are evolutionarily linked to the progenitors of thermonuclear supernovae and
are expected to be strong Galactic sources of gravitational waves detectable to
upcoming space-based interferometers. AM CVn binaries with orbital periods
20--23 min exist in a constant high state with a permanently ionised
accretion disc. We present the discovery of TIC 378898110, a bright (
mag), nearby ( pc), high-state AM CVn binary discovered in TESS
two-minute-cadence photometry. At optical wavelengths this is the
third-brightest AM CVn binary known. The photometry of the system shows a
23.07172(6) min periodicity, which is likely to be the `superhump' period and
implies an orbital period in the range 22--23 min. There is no detectable
spectroscopic variability. The system underwent an unusual, year-long
brightening event during which the dominant photometric period changed to a
shorter period (constrained to min), which we suggest may be
evidence for the onset of disc-edge eclipses. The estimated mass transfer rate,
, is
unusually high and may suggest a high-mass or thermally inflated donor. The
binary is detected as an X-ray source, with a flux of erg cm s in the 0.3--10 keV range. TIC 378898110
is the shortest-period binary system discovered with TESS, and its large
predicted gravitational-wave amplitude makes it a compelling verification
binary for future space-based gravitational wave detectors.Comment: 15 pages, 14 figures. Accepted to MNRA
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta
We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the Southern Astrophysical Research and Magellan telescopes; the UV spectrum was obtained with the Hubble Space Telescope at 5.5 days. Our data reveal a rapidly fading blue component (T ≈ 5500 K at 1.5 days) that quickly reddens; spectra later than ≳4.5 days peak beyond the optical regime. The spectra are mostly featureless, although we identify a possible weak emission line at ∼7900 Å; at t ≲ 4.5 days. The colors, rapid evolution, and featureless spectrum are consistent with a "blue" kilonova from polar ejecta comprised mainly of light r-process nuclei with atomic mass number A ≲ 140. This indicates a sightline within θobs ≲ 45° of the orbital axis. Comparison to models suggests ∼0.03 M o of blue ejecta, with a velocity of . The required lanthanide fraction is ∼10-4, but this drops to <10-5in the outermost ejecta. The large velocities point to a dynamical origin, rather than a disk wind, for this blue component, suggesting that both binary constituents are neutron stars (as opposed to a binary consisting of a neutron star and a black hole). For dynamical ejecta, the high mass favors a small neutron star radius of ≲12 km. This mass also supports the idea that neutron star mergers are a major contributor to r-process nucleosynthesis.La lista completa de autores que integran el documento puede consultarse en el archivoInstituto de Astrofísica de La Plat
Satisfação no trabalho da equipe de enfermagem: revisão integrativa
Job satisfaction consists of a feeling of wellbeing, resulting from the interaction of several occupational aspects, and may influence the worker's relationship with the organization, clients and family. Hence, it becomes important for the quality of nursing care to reflect on this topic in depth. Therefore, this study aimed to examine the scientific evidence related to job satisfaction in Brazilian nursing. An integrative literature review was carried out in the databases LILACS, MEDLINE, BDENF and Cochrane Library, totaling 17 publications, categorized in: Job Satisfaction, Job Dissatisfaction and Associated Factors. It was concluded that job satisfaction is determined by a complex network of factors and may vary depending on the group studied. Additional research, particularly of evidence level III in different nursing fields, covering all of Brazil, is necessary to support the implementation of occupational improvements.La satisfacción en el trabajo consiste en un sentimiento de bienestar resultante de la interacción de varios aspectos ocupacionales, pudiendo influenciar la relación del trabajador con la organización, clientes y familia. Es importante para la calidad de la asistencia de enfermería realizar una reflexión profunda sobre este tema, por eso se objetivó en este estudio analizar las evidencias científicas referentes a la satisfacción en el trabajo del equipo de enfermería brasileño. Se trató de una revisión integradora de la literatura en las bases de datos LILACS, MEDLINE, BDENF y Biblioteca Cochrane, totalizando 17 publicaciones categorizadas en: Satisfacción en el Trabajo, Insatisfacción en el Trabajo y Factores Asociados. Se concluyó que la satisfacción en el trabajo es determinada por una red compleja de factores, pudiendo variar conforme el grupo estudiado. Investigaciones adicionales, especialmente con niveles de evidencias III, en diferentes campos de actuación de la enfermería, abarcando todo el Brasil, son necesarias para subsidiar la implantación de mejorías ocupacionales.A satisfação no trabalho consiste em sentimento de bem-estar. resultante da interação de vários aspectos ocupacionais, podendo influenciar a relação do trabalhador com a organização, clientes e família. Torna-se importante, para a qualidade da assistência de enfermagem, reflexão aprofundada sobre esse tema, e, por isso, objetivou-se neste estudo analisar as evidências científicas referentes à satisfação no trabalho da equipe de enfermagem brasileira. Trata-se de revisão integrativa da literatura nas bases de dados LILACS, MEDLINE, BDENF e Biblioteca Cochrane, totalizando 17 publicações categorizadas em: satisfação no trabalho, insatisfação no trabalho e fatores associados. Conclui-se que a satisfação no trabalho é determinada por rede complexa de fatores, podendo variar conforme o grupo estudado. Pesquisas adicionais, especialmente com níveis de evidências III, em diferentes campos de atuação da enfermagem, abrangendo todo Brasil, são necessárias para subsidiar a implantação de melhorias ocupacionais
A rotating white dwarf shows different compositions on its opposite faces
White dwarfs, the extremely dense remnants left behind by most stars after
their death, are characterised by a mass comparable to that of the Sun
compressed into the size of an Earth-like planet. In the resulting strong
gravity, heavy elements sink toward the centre and the upper layer of the
atmosphere contains only the lightest element present, usually hydrogen or
helium. Several mechanisms compete with gravitational settling to change a
white dwarf's surface composition as it cools, and the fraction of white dwarfs
with helium atmospheres is known to increase by a factor ~2.5 below a
temperature of about 30,000 K; therefore, some white dwarfs that appear to have
hydrogen-dominated atmospheres above 30,000 K are bound to transition to be
helium-dominated as they cool below it. Here we report observations of ZTF
J203349.8+322901.1, a transitioning white dwarf with two faces: one side of its
atmosphere is dominated by hydrogen and the other one by helium. This peculiar
nature is likely caused by the presence of a small magnetic field, which
creates an inhomogeneity in temperature, pressure or mixing strength over the
surface. ZTF J203349.8+322901.1 might be the most extreme member of a class of
magnetic, transitioning white dwarfs -- together with GD 323, a white dwarf
that shows similar but much more subtle variations. This new class could help
shed light on the physical mechanisms behind white dwarf spectral evolution.Comment: 45 pages, 11 figure
SDSS DR7 white dwarf catalog
We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20,407 white dwarf spectra, representing 19,712 stars, and provide atmospheric model fits to 14,120 DA and 1011 DB white dwarf spectra from 12,843 and 923 stars, respectively. These numbers represent more than a factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalogs based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated log g if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.Facultad de Ciencias Astronómicas y Geofísica
The 40 pc sample of white dwarfs from Gaia
We present a comprehensive overview of a volume-complete sample of white dwarfs located within 40 pc of the Sun, a significant proportion of which were detected in Gaia Data Release 3 (DR3). Our DR3 sample contains 1076 spectroscopically confirmed white dwarfs, with just five candidates within the volume remaining unconfirmed (> 99 per cent spectroscopic completeness). Additionally, 28 white dwarfs were not in our initial selection from Gaia DR3, most of which are in unresolved binaries. We use Gaia DR3 photometry and astrometry to determine a uniform set of white dwarf parameters, including mass, effective temperature, and cooling age. We assess the demographics of the 40 pc sample, specifically magnetic fields, binarity, space density, and mass distributions
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta
We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the Southern Astrophysical Research and Magellan telescopes; the UV spectrum was obtained with the Hubble Space Telescope at 5.5 days. Our data reveal a rapidly fading blue component (T ≈ 5500 K at 1.5 days) that quickly reddens; spectra later than ≳4.5 days peak beyond the optical regime. The spectra are mostly featureless, although we identify a possible weak emission line at ∼7900 Å; at t ≲ 4.5 days. The colors, rapid evolution, and featureless spectrum are consistent with a "blue" kilonova from polar ejecta comprised mainly of light r-process nuclei with atomic mass number A ≲ 140. This indicates a sightline within θobs ≲ 45° of the orbital axis. Comparison to models suggests ∼0.03 M o of blue ejecta, with a velocity of . The required lanthanide fraction is ∼10-4, but this drops to <10-5in the outermost ejecta. The large velocities point to a dynamical origin, rather than a disk wind, for this blue component, suggesting that both binary constituents are neutron stars (as opposed to a binary consisting of a neutron star and a black hole). For dynamical ejecta, the high mass favors a small neutron star radius of ≲12 km. This mass also supports the idea that neutron star mergers are a major contributor to r-process nucleosynthesis.La lista completa de autores que integran el documento puede consultarse en el archivoInstituto de Astrofísica de La Plat
- …