29 research outputs found
The eclipsing Cataclysmic Variable GS Pavonis: Evidence for disk radius changes
We have obtained differential time series photometry of the cataclysmic
variable GS Pavonis over a timespan of 2 years. These show that this system is
deeply eclipsing (~2-3.5 mag) with an orbital period of 3.72 hr. The eclipse
depth and out-of-eclipse light levels are correlated. From this correlation we
deduce that the disk radius is changing and that the eclipses in the low state
are total. The derived distance to GS Pav is 790+/-90 pc, with a height above
the galactic plane of 420+/-60 pc. We classify GS Pav as a novalike system.Comment: 4 pages, including 2 figures, accepted for publication in A&A Letter
Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes
We present observations of the interstellar interloper 1I/2017 U1 ('Oumuamua)
taken during its 2017 October flyby of Earth. The optical colors B-V =
0.700.06, V-R = 0.450.05, overlap those of the D-type Jovian Trojan
asteroids and are incompatible with the ultrared objects which are abundant in
the Kuiper belt. With a mean absolute magnitude = 22.95 and assuming a
geometric albedo = 0.1, we find an average radius of 55 m. No coma is
apparent; we deduce a limit to the dust mass production rate of only
210 kg s, ruling out the existence of exposed ice
covering more than a few m of the surface. Volatiles in this body, if they
exist, must lie beneath an involatile surface mantle 0.5 m thick,
perhaps a product of prolonged cosmic ray processing in the interstellar
medium. The lightcurve range is unusually large at 2.00.2
magnitudes. Interpreted as a rotational lightcurve the body has semi-axes
230 m 35 m. A 6:1 axis ratio is extreme relative to most
small solar system asteroids and suggests that albedo variations may
additionally contribute to the variability. The lightcurve is consistent with a
two-peaked period 8.26 hr but the period is non-unique as a result of
aliasing in the data. Except for its unusually elongated shape, 1I/2017 U1 is a
physically unremarkable, sub-kilometer, slightly red, rotating object from
another planetary system. The steady-state population of similar, 100 m
scale interstellar objects inside the orbit of Neptune is 10, each
with a residence time 10 yr.Comment: 25 Pages, 2 Tables, 7 Figures; submitted to ApJ
A Survey of Eclipsing Binary Stars in the Eastern Spiral Arm of M31
Results of an archival survey are presented using B-band imaging of the
eastern spiral arm of M31. Focusing on the eclipsing binary star population, a
matched-filter technique has been used to identify 280 binary systems. Of
these, 127 systems (98 of which are newly discovered) have sufficient phase
coverage to allow accurate orbital periods to be determined. At least nine of
these binaries are detached systems which could, in principle, be used for
distance determination. The light curves of the detached and other selected
systems are presented along with a discussion of some of the more interesting
binaries. The impact of unresolved stellar blends on these lightcurves is
considered.Comment: 10 pages, accepted for publication in MNRA
1RXS J232953.9+062814: A Dwarf Nova with a 64-minute Orbital Period and a Conspicuous Secondary Star
We present spectroscopy and time-series photometry of the newly discovered
dwarf nova 1RXS J232953.9+062814. Photometry in superoutburst reveals a
superhump with a period of 66.06(6) minutes. The low state spectrum shows
Balmer and HeI emission on a blue continuum, and in addition shows a rich
absorption spectrum of type K4 +- 2. The absorption velocity is modulated
sinusoidally at P_orb = 64.176(5) min, with semi-amplitude K = 348(4) km/s. The
low-state light curve is double-humped at this period, and phased as expected
for ellipsoidal variations. The absorption strength does not vary appreciably
around the orbit. The orbital period is shorter than any other cataclysmic
variable save for a handful of helium-star systems and V485 Centauri (59
minutes). The secondary is much hotter than main sequence stars of similar
mass, but is well-matched by helium-enriched models, indicating that the
secondary evolved from a more massive progenitor. A preliminary calculation in
which a 1.2 solar-mass star begins mass transfer near the end of H burning
matches this system's characteristics remarkably well.Comment: accepted to Astrophysical Journal Letters; 14 pages, 3 eps figures +
1 jpg greyscale figur
Superhumps in Cataclysmic Binaries. XXII. 1RXS J232953.9+062814
We report photometry of 1RXS J232953.9+062814, a recently discovered dwarf
nova with a remarkably short 64.2-minute orbital period. In quiescence, the
star's light curve is that of a double sinusoid, arising from the "ellipsoidal"
distortion of the Roche-lobe-filling secondary. During superoutburst, common
superhumps develop with a period 3-4% longer than P_orb. This indicates a mass
ratio M_2/M_1=0.19+-0.02, a surprisingly large value in so compact a binary.
This implies that the secondary star has a density 2-3 times higher than that
of other short-period dwarf novae, suggesting a secondary enriched by H-burning
prior to the common-envelope phase of evolution. We estimate i=50+-5 deg,
M_1=0.63 (+0.12, -0.09) M_sol, M_2=0.12 (+0.03, -0.02) M_sol, R_2=0.121
(+0.010, -0.007) R_sol, and a distance to the binary of 180+-40 pc.Comment: PDF, 17 pages, 3 tables, 5 figures; accepted, in press, to appear
June 2002, PASP; more info at http://cba.phys.columbia.edu
Superhumps in Cataclysmic Binaries. XXV. q_crit, epsilon(q), and Mass-Radius
We report on successes and failures in searching for positive superhumps in
cataclysmic variables, and show the superhumping fraction as a function of
orbital period. Basically, all short-period systems do, all long-period systems
don't, and a 50% success rate is found at P_orb=3.1+-0.2 hr. We can use this to
measure the critical mass ratio for the creation of superhumps. With a
mass-radius relation appropriate for cataclysmic variables, and an assumed mean
white-dwarf mass of 0.75 M_sol, we find a mass ratio q_crit=0.35+-0.02.
We also report superhump studies of several stars of independently known mass
ratio: OU Virginis, XZ Eridani, UU Aquarii, and KV UMa (= XTE J1118+480). The
latter two are of special interest, because they represent the most extreme
mass ratios for which accurate superhump measurements have been made. We use
these to improve the epsilon(q) calibration, by which we can infer the elusive
q from the easy-to-measure epsilon (the fractional period excess of P_superhump
over P_orb). This relation allows mass and radius estimates for the secondary
star in any CV showing superhumps. The consequent mass-radius law shows an
apparent discontinuity in radius near 0.2 M_sol, as predicted by the disrupted
magnetic braking model for the 2.1-2.7 hour period gap. This is effectively the
"empirical main sequence" for CV secondaries.Comment: PDF, 45 pages, 9 tables, 12 figures; accepted, in press, to appear
November 2005, PASP; more info at http://cba.phys.columbia.edu
The metamorphosis of SN1998bw
We present and discuss the photometric and spectroscopic evolution of the
peculiar SN1998bw, associated with GRB980425, through an analysis of optical
and near IR data collected at ESO-La Silla. The spectroscopic data, spanning
the period from day -9 to day +376 (relative to B maximum), have shown that
this SN was unprecedented, although somewhat similar to SN1997ef. Maximum
expansion velocities as high as 3x10^4 km/s to some extent mask its resemblance
to other Type Ic SNe. At intermediate phases, between photospheric and fully
nebular, the expansion velocities (~10^4 km/s) remained exceptionally high
compared to those of other recorded core-collapse SNe at a similar phase. The
mild linear polarization detected at early epochs suggests the presence of
asymmetry in the emitting material. The degree of asymmetry, however, cannot be
decoded from these measurements alone. The HeI 1.083 mu and 2.058 mu lines are
identified and He is suggested to lie in an outer region of the envelope. The
temporal behavior of the fluxes and profiles of emission lines of MgI]4571A,
[OI]6300,6364A and a feature ascribed to Fe are traced to stimulate future
modeling work.Comment: 32 pages, 19 figures; ps file including figures at
http://www.eso.org/~fpatat/sn98b