375 research outputs found
Is FIRST J102347.6+003841 Really a Cataclysmic Binary?
The radio source FIRST J102347.6+003841 was presented as the first
radio-selected cataclysmic. In the discovery paper, Bond et al. (2002) show a
spectrum consistent with a magnetic AM Her-type system and a light curve with
rapid, irregular flickering. In contrast, Woudt, Warner, and Pretorius (2004)
found a smoothly-varying light curve with a period near 4.75 h and one minimum
per orbit, indicating a dramatic change. We present time-resolved spectra
showing a superficially normal, mid-G type photosphere, with no detectable
emission lines. The absorption-line radial velocity varies sinusoidally, with
semi-amplitude 268 +- 4 km/s, on the orbital period, which is refined to
0.198094(2) d. At this orbital period the secondary's spectral type is
atypically early, suggesting an unusual evolutionary history. We also obtained
BVI photometry around the orbit. The light curve resembles that given by Woudt
et al., and the color modulation is consistent with a heating effect. A simple
illumination model matches the observations strikingly well with a Roche-lobe
filling secondary near 5650 kelvin being illuminated by a primary giving out
around 2 solar luminosities. The modest amplitude of the observed modulation
constrains the orbital inclination to be less than about 55 deg, unless the
gravity darkening is artificially reduced. The resulting primary star mass is
above the Chandrasekhar limit (assuming conventional gravity darkening). We
examine the possibility that the compact object in this system is not a white
dwarf, in which case this is not actually a cataclysmic variable. On close
examination, FIRST J102347.6+003841 defies easy classification.Comment: 24 pages, 5 postscript and two JPG figures; Astronomical Journal,
accepte
Serendipitous Discovery and Parallax of a Nearby L Dwarf
A field star serendipitously observed in a parallax program proved to have a
proper motion of 562 mas/yr and a parallax of 82 +- 2 mas. The star is
identified with 2MASS J07003664+3157266. A Keck LRIS spectrum shows its
spectral type to be L3.5, as expected from its infrared and optical colors and
absolute magnitude. This object had not been previously recognized as an L
dwarf, perhaps because of crowding at its relatively low Galactic latitude (b =
+15.8 degrees).Comment: PASP, in press. 8 pages incl.2 postscript figures, plus one jpeg
figur
Aquila X--1: a low inclination soft X-ray transient
We have obtained I-band photometry of the neutron star X-ray transient Aql
X--1 during quiescence. We find a periodicity at 2.487 cd-1, which we interpret
as twice the orbital frequency (19.30+/-0.05 h). Folding the data on the
orbital period, we model the light curve variations as the ellipsoidal
modulation of the secondary star. We determine the binary inclination to be
20--31 degrees (90 per cent confidence) and also 95 per cent upper limits to
the radial velocity semi-amplitude and rotational broadening of the secondary
star to be 117 kms-1 and 50 kms-1 respectively.Comment: 4 pages text, 3 figures, to appear in MNRA
A Newly-Discovered Cataclysmic Binary Near the ROSAT Galactic Plane Source RX J1910.8+2856
We report the discovery of a new cataclysmic binary star from the ROSAT Galactic Plane Survey. The star has V \u3e∼ 18.5atminimumlightandwehavemeasureditasbrightasV = 15.7. Spectroscopy shows broad hydrogen and helium emission lines; HeII λ4686 is not detected. Hα radial velocities yield an orbital period of 0.1429 ± 0.0004 d (3.430 ± 0.010 h). Time- series photometry covering one orbital cycle near maximum light shows irregular variability, but no evidence of an eclipse. ThesystemappearstobeanewdwarfnovaoftheUGemorZ Cam type, and is unlikely to be a magnetic system. Its period is unusually short for a U Gem star.
Curiously, the new cataclysmic binary is 83′′ from the orig- inal ROSAT PSPC survey position, which puts it outside the PSPC positional uncertainty. Follow-up observations with the HRI reveal that the PSPC source is the superposition of two sources, and the cataclysmic is much the weaker of the two in X-rays. Its discovery in this survey is therefore essentially acci- dental. A V = 19.4 mag star is located 1.2′′ from the stronger source’s HRI position
GRB 060218/SN 2006aj: A Gamma-Ray Burst and Prompt Supernova at z=0.0335
We report the imaging and spectroscopic localization of GRB 060218 to a
low-metallicity dwarf starburst galaxy at z = 0.03345 +/- 0.00006. In addition
to making it the second nearest gamma-ray burst known, optical spectroscopy
reveals the earliest detection of weak, supernova-like Si II near 5720
Angstroms (0.1c), starting 1.95 days after the burst trigger. UBVRI photometry
obtained between 1 and 26 days post-burst confirms the early rise of supernova
light, and suggests a short time delay between the gamma-ray burst and the
onset of SN 2006aj if the early appearance of a soft component in the X-ray
spectrum is understood as a ``shock breakout''. Together, these results verify
the long-hypothesized origin of soft gamma-ray bursts in the deaths of massive
stars.Comment: 5 pages, 2 figure
Spectroscopy and Orbital Periods of the Old Novae V533 Herculis, V446 Herculis and X Serpentis
We report spectroscopic orbital periods of 0.147 d (= 3.53 h) for V533 Her, 0.207 d (= 4.97 h) for V446 Her and 1.478 d for X Ser. V533 Her (Nova Herculis 1963) shows absorption features in its He i and Balmer lines which appear only in a limited range of orbital phase, suggesting that it is a low-inclination SW Sextantis star. V446 Her is unusual in that it has started normal dwarf nova eruptions after a nova outburst, but we find nothing else unusual about it — in particular, a distance estimate based on its dwarf nova outbursts agrees nicely with another based on the rate of decline of its nova eruption, both giving d ∼ 1 kpc. In X Ser, unlike in other old novae with long periods, no spectral features of the secondary star are visible. This and its outburst magnitude both suggest that it is quite distant and luminous, and at least 1 kpc from the Galactic plane
The Long-Period Orbit of the Dwarf Nova V630 Cassiopeiae
We present extensive spectroscopy and photometry of the dwarf nova V630 Cassiopeiae. A late-type (K4-5) absorption spectrum is easily detectable, from which we derive the orbital parameters. We find a spectroscopic period of P=2.56387 +/- (4 times 10^{-5}) days and a semiamplitude of K_2=132.9 +/- 4.0 km/s. The resulting mass function, which is a firm lower limit on the mass of the white dwarf, is then f(M)=0.624 +/- 0.056 solar masses. The secondary star is a ``stripped giant\u27\u27, and using relations between the core mass and the luminosity and the core mass and the radius we derive a lower limit of M_2 \u3e 0.165 solar masses for the secondary star. The rotational velocity of the secondary star is not resolved in our spectra and we place a limit of V_rot*sin(i) \u3c 40 km/s. The long-term light curve shows variations of up to 0.4 mag on short (1-5 days) time scales, and variations of 0.2-0.4 mag on longer (3-9 months) time scales. In spite of these variations, the ellipsoidal light curve of the secondary star is easily seen when the data are folded on the spectroscopic ephemeris. Ellipsoidal models fit to the mean light curve give an inclination in the range 66.96 \u3c i \u3c 78.08 degrees (90 per cent confidence). This inclination range, and the requirement that M_2 \u3e 0.165 solar masses and V_rot*sin(i) \u3c 40 km/s yields a white dwarf mass of M_1=0.977^{+0.168}_{-0.098} solar masses and a secondary star mass of M_2=0.172^{+0.029}_{-0.012} solar masses (90 per cent confidence limits). Our findings confirm the suggestion of Warner (1994), namely that V630 Cas is rare example of a dwarf nova with a long orbital period
V405 Peg (RBS 1955): A Nearby, Low-Luminosity Cataclysmic Binary
(Abridged). The cataclysmic binary V405 Peg, originally discovered as ROSAT
Bright Source (RBS) 1955 (= 1RXS J230949.6+213523), shows a strong contribution
from a late-type secondary star in its optical spectrum, which led Schwope et
al. to suggest it to be among the nearest cataclysmic binaries. We present
extensive optical observations of V405 Peg. Time-series spectroscopy shows the
orbital period, Porb, to be 0.1776469(7) d (= 4.2635 hr), or 5.629 cycle/d. We
classify the secondary as M3 - M4.5. Astrometry with the MDM 2.4m telescope
gives a parallax 7.2 +- 1.1 milli-arcsec, and a relative proper motion of 58
mas/yr. Our best estimate of the distance yields d = 149 (+26, -20) pc. The
secondary stars's radial velocity has K2 = 92 +- 3 km/s, indicating a fairly
low orbital inclination if the masses are typical. Extensive I-band time-series
observations in the show the system varying between a minimum brightness level
of I = 14.14 and states of enhanced activity about 0.2 mag brighter. While the
low-state shows an ellipsoidal modulation, an additional photometric modulation
appears in the high state, with 0.1 mag amplitude and period 220-280 min. The
frequency of this modulation appears to be stable for a month or so, but no
single period was consistently detected from one observing season to the next.
We estimate the system luminosity by combining optical measurements with the
archival X-ray spectrum. The implied mass accretion rate is orders of
magnitudes below the predictions for the standard angular momentum loss above
the period gap. The system may possibly belong to a largely undiscovered
population of hibernating CVs.Comment: 11 figures; 7 of these are .png or .jpg to save space. In press for
Publications of the Astronomical Society of the Pacifi
XMM-Newton observations of the low-luminosity cataclysmic variable V405 Pegasi
V405 Peg is a low-luminosity cataclysmic variable (CV) that was identified as
the optical counterpart of the bright, high-latitude ROSAT all-sky survey
source RBS1955. The system was suspected to belong to a largely undiscovered
population of hibernating CVs. Despite intensive optical follow-up its subclass
however remained undetermined.
We want to further classify V405 Peg and understand its role in the CV zoo
via its long-term behaviour, spectral properties, energy distribution and
accretion luminosity.
We perform a spectral and timing analysis of \textit{XMM-Newton} X-ray and
ultra-violet data. Archival WISE, HST, and Swift observations are used to
determine the spectral energy distribution and characterize the long-term
variability.
The X-ray spectrum is characterized by emission from a multi-temperature
plasma. No evidence for a luminous soft X-ray component was found. Orbital
phase-dependent X-ray photometric variability by occurred without
significant spectral changes. No further periodicity was significant in our
X-ray data. The average X-ray luminosity during the XMM-Newton observations was
L_X, bol simeq 5e30 erg/s but, based on the Swift observations, the
corresponding luminosity varied between 5e29 erg/s and 2e31 erg/son timescales
of years.
The CV subclass of this object remains elusive. The spectral and timing
properties show commonalities with both classes of magnetic and non-magnetic
CVs. The accretion luminosity is far below than that expected for a standard
accreting CV at the given orbital period. Objects like V405 Peg might represent
the tip of an iceberg and thus may be important contributors to the Galactic
Ridge X-ray Emission. If so they will be uncovered by future X-ray surveys,
e.g. with eROSITA.Comment: A&A, in pres
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