963 research outputs found
IUE observations of a hot DAO white dwarf: Implications for diffusion theory and photospheric stratification
Observations of the DAO white dwarf PG1210+533, including the first high dispersion spectrum of a hybrid H-He object of this nature were obtained by IUE. In contrast with hot DAs in the 50,000 K temperature range, PG1210+533 shows no narrow interstellar-like metal lines, in spite of an optically observed He/H abundance of 0.1. This lack of metal makes accretion from the ISM an unlikely source for the He in the PG1210+533 photosphere. A significant discovery in the high dispersion spectrum is the existence of a sharp, non-LTE like, core seen in the He II 1640 line. Such features are detected in DO white dwarfs. A small aperture SWP low dispersion observation reveals the Lyman alpha profile of PG1210+533 to be surprisingly weak and narrow. Fits of this profile using pure H models yielded a T(eff) = 56,000 K. Fits of the Balmer H gamma profile however, yield T(eff) = 42,300 K and log g = 8.5 + or - 0.5 for the same models. It is unlikely that homogeneously mixed H-He atmospheres can resolve the inconsistency between the Lyman alpha and H gamma features in this star. Stratified models involving thin H photospheres may be necessary to explain these results
HST Spectra of GW Librae: A Hot Pulsating White Dwarf in a Cataclysmic Variable
We have obtained Hubble Space Telescope UV spectra of the white dwarf in GW
Lib, the only known non-radially pulsating white dwarf in a cataclysmic
variable, and the first known DAZQ variable. The UV light curve reveals large
amplitude (10%) pulsationsin the UV with the same periods (646, 376 and 237 s)
as those seen at optical wavelengths, but the mean spectrum fits with an
average white dwarf temperature (14,700K for a 0.6M_{odot} white dwarf) that is
too hot to be in the normal instability strip for ZZ Ceti stars. A better fit
is achieved with a dual temperature model (with 63% of the white dwarf surface
at a temperature of 13300K and 37% at 17100K), and a higher mass (0.8M_{odot})
white dwarf with 0.1 solar metal abundance. Since the blue edge of the
instability strip moves to higher temperature with increasing mass, the lower
temperature of this model is within the instability strip. However, the
presence of accretion likely causes abundance and atmospheric temperature
differences in GW Lib compared to all known single white dwarf pulsators, and
the current models that have been capable of explaining ZZ Ceti stars may not
apply.Comment: 13 pages, 4 figure
PENGARUH PENDIDIKAN DAN PELATIHAN, DISIPLIN KERJA SERTA MOTIVASI KERJA TERHADAP KINERJA PEGAWAI DI BADAN KEPEGAWAIAN DAERAH KABUPATEN KOTAWARINGIN TIMUR
Tujuan penelitian ini adalah untuk mendeskripsi dan menganalisis pengaruh pendidikan dan pelatihan, disiplin kerja, motivasi kerja baik secara parsial maupun simultan terhadap kinerja pegawai di Badan Kepegawaian Daerah Kabupaten Kotawaringin Timur. Metode penelitian yang digunakan dalam penelitian ini menggunakan metode kuantitatif dengan menggunakan sampel sebanyak 36 orang pegawai yang ada di Badan Kepegawaian Daerah Kabupaten Kotawaringin Timur. Teknik pengambilan sampel yang digunakan dalam penelitian ini menggunakan sampling jenuh, teknik pengumpulan data menggunakan kuesioner / angket dengan cara memberikan seperangkat pertanyaan kepada responden, analisis data menggunakan regresi linear berganda. Hasil uji secara parsial variabel Pendidikan dan Pelatihan (X1) diperoleh nilai signifikansi sebesar 0,771 > 0,05 dan nilai thitung 0,293 < ttabel 2,036, dengan demikian Pendidikan dan Pelatihan tidak berpengaruh signifikan terhadap kinerja pegawai, variabel Disiplin Kerja (X2) diperoleh nilai signifikansi sebesar 0,002 < 0,05 dan nilai thitung 3,457 > ttabel 2,036, dengan demikian disiplin kerja berpengaruh signifikan terhadap kinerja pegawai, variabel Motivasi Kerja (X3) diperoleh nilai signifikansi sebesar 0,122 > 0,05 dan nilai thitung 1,590 < ttabel 2,036, dengan demikian motivasi kerja tidak berpengaruh signifikan terhadap kinerja pegawai. Hasil uji secara simultan diperoleh nilai signifikansi sebesar 0,000 < 0,05 dan nilai Fhitung 11,999 > Ftabel 2,90, dengan demikian Pendidikan dan Pelatihan, Disiplin Kerja, dan Motivasi Kerja secara simultan (bersama-sama) berpengaruh siginikan terhadap Kinerja Pegawai dengan kontribusi sebesar 52,9% sedangkan sisanya sebear 47,1% dipengaruhi oleh variabel lain di luar variabel yang tidak diteliti
ST/STIS Spectroscopy of the White Dwarfs in the Short-Period Dwarf Novae LL And and EF Peg
We present new HST/STIS observations of the short-period dwarf novae LL And
and EF Peg during deep quiescence. We fit stellar models to the UV spectra and
use optical and IR observations to determine the physical parameters of the
whitedwarfs in the systems, the distances to the binaries, and the properties
of thesecondary stars. Both white dwarfs are relatively cool, having T_{eff}
near 15000K, and consistent with a mass of 0.6 M-sun. The white dwarf in LL And
appears to be of solar abundance or slightly lower while that in EF Peg is near
0.1-0.3 solar. LL And is found to be 760 pc away while EF Peg is closer at 380
pc. EF Peg appears to have an ~M5V secondary star, consistent with that
expected for its orbital period, while the secondary object in LL And remains a
mystery.Comment: Accepted in Ap
HST/STIS spectroscopy of the exposed white dwarf in the short-period dwarf nova EK TrA
We present high resolution Hubble Space Telescope ultraviolet spectroscopy of
the dwarf nova EK TrA obtained in deep quiescence. The Space Telescope Imaging
Spectrograph data reveal the broad Ly-alpha absorption profile typical of a
moderately cool white dwarf, overlayed by numerous broad emission lines of He,
C, N, and Si and by a number of narrow absorption lines, mainly of CI and SiII.
Assuming a white dwarf mass in the range 0.3-1.4Msun we derive
Teff=17500-23400K for the primary in EK TrA; Teff=18800K for a canonical mass
of 0.6Msun. From the narrow photospheric absorption lines, we measure the white
dwarf rotational velocity, v*sin i=200+-100kms. Even though the strong
contamination of the photospheric white dwarf absorption spectrum by the
emission lines prevents a detailed quantitative analysis of the chemical
abundances of the atmosphere, the available data suggest slightly sub-solar
abundances. The high time resolution of the STIS data allows us to associate
the observed ultraviolet flickering with the emission lines, possibly
originating in a hot optically thin corona above the cold accretion disk.Comment: 6 pages A&A-Latex, 5 Figures, accepted for publication in A&
The White Dwarfs within 25 Parsecs of the Sun: Kinematics and Spectroscopic Subtypes
We present the fractional distribution of spectroscopic subtypes, range and
distribution of surface temperatures, and kinematical properties of the white
dwarfs within 25pc of the sun. There is no convincing evidence of halo white
dwarfs in the total 25 pc sample of 224 white dwarfs. There is also little to
suggest the presence of genuine thick disk subcomponent members within 25
parsecs. It appears that the entire 25 pc sample likely belong to the thin
disk. We also find no significant kinematic differences with respect to
spectroscopic subtypes. The total DA to non-DA ratio of the 25 pc sample is
1.8, a manifestation of deepening envelope convection which transforms DA stars
with sufficiently thin H surface layers into non-DAs. We compare this ratio
with the results of other studies. We find that at least 11% of the white
dwarfs within 25 parsecs of the sun (the DAZ and DZ stars) have photospheric
metals that likely originate from accretion of circumstellar material (debris
disks) around them. If this interpretation is correct, then it suggests the
possibility that a similar percentage have planets, asteroid-like bodies or
debris disks orbiting them. Our volume-limited sample reveals a pileup of DC
white dwarfs at the well-known cutoff in DQ white dwarfs at Tef about 6000K.
Mindful of small number statistics, we speculate on its possible evolutionary
significance. We find that the incidence of magnetic white dwarfs in the 25 pc
sample is at least 8%, in our volume-limited sample, dominated by cool white
dwarfs. We derive approximate formation rates of DB and DQ degenerates and
present a preliminary test of the evolutionary scenario that all cooling DB
stars become DQ white dwarfs via helium convective dredge-up with the diffusion
tail of carbon extending upward from their cores.Comment: Accepted for publication in The Astronomical Journa
Hubble space telescope STIS spectroscopy of the peculiar nova-like variables BK Lyn, V751 Cygni, and V380 Oph
We obtained Hubble STIS spectra of three nova-like variables: V751 Cygni, V380 Oph, andâthe only confirmed nova-like variable known to be below the period gapâBK Lyn. In all three systems, the spectra were taken during high optical brightness state, and a luminous accretion disk dominates their far-ultraviolet (FUV) light. We assessed a lower limit of the distances by applying the infrared photometric method of Knigge. Within the limitations imposed by the poorly known system parameters (such as the inclination, white dwarf mass, and the applicability of steady state accretion disks) we obtained satisfactory fits to BK Lyn using optically thick accretion disk models with an accretion rate of for a white dwarf mass of Mwd = 1.2M and for Mwd = 0.4M. However, for the VY Scl-type nova-like variable V751 Cygni and for the SW Sex star V380 Oph, we are unable to obtain satisfactory synthetic spectral fits to the high state FUV spectra using optically thick steady state accretion disk models. The lack of FUV spectra information down to the Lyman limit hinders the extraction of information about the accreting white dwarf during the high states of these nova-like systems
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