220 research outputs found
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
HS 2331+3905: The Cataclysmic Variable That Has It All
We report detailed follow-up observations of the cataclysmic variable HS 2331+3905, identified as an emission- line object in the Hamburg Quasar Survey. An orbital period of 81.08 min is unambiguously determined from the detection of eclipses in the light curves of HS 2331+3905. A second photometric period is consistently detected at P â 83.38 min, âŒ2.8% longer than Porb, which we tentatively relate to the presence of permanent superhumps. High time resolution photometry exhibits short-timescale variability on time scales of â5â6 min which we interpret as non-radial white dwarf pulsations, as well as a coherent signal at 1.12 min, which is likely to be the white dwarf spin period. A large-amplitude quasi-sinusoidal radial velocity modulation of the Balmer and Helium lines with a period âŒ3.5 h is persistently detected throughout three seasons of time-resolved spectroscopy. However, this spectroscopic period, which is in no way related to the orbital period, is not strictly coherent but drifts in period and/or phase on time scales of a few days. Modeling the far-ultraviolet to infrared spectral energy distribution of HS 2331+3905, we determine a white dwarf temperature of Teff â 10 500 K (assuming Mwd = 0.6 Mâ), close to the ZZ Ceti instability strip of single white dwarfs. The spectral model implies a distance of d = 90 ± 15 pc, and a low value for the distance is supported by the large proper motion of the system, ÎŒ = 0.14âČâČ yrâ1. The non-detection of molecular bands and the low J, H, and K fluxes of HS 2331+3905 make this object a very likely candidate for a brown-dwarf donor
The Post-Common Envelope and Pre-Cataclysmic Binary PG 1224+309
We have made extensive spectroscopic and photometric observations of PG
1224+309, a close binary containing a DA white dwarf primary and an M4+
secondary. The H alpha line is in emission due to irradiation of the M-star by
the hot white dwarf and is seen to vary around the orbit. From the radial
velocities of the H alpha line we derive a period of P = 0.258689 +/- 0.000004
days and a semi-amplitude of K_Halpha = 160 +/- 8 km/s. We estimate a
correction Delta_K = 21 +/- 2 km/s, where K_M = K_Halpha + Delta_K. Radial
velocity variations of the white dwarf reveal a semi-amplitude of K_WD = 112
+/- 14 km/s. The blue spectrum of the white dwarf is well fit by a synthetic
spectrum having T_eff = 29,300 K and log(g) = 7.38. The white dwarf contributes
97% of the light at 4500 Angstroms and virtually all of the light blueward of
3800 Angstroms. No eclipses are observed. The mass inferred for the white dwarf
depends on the assumed mass of the thin residual hydrogen envelope: 0.40 < M_WD
< 0.45 solar masses for hydrogen envelope masses of 0 < M_H < 4.0E-4 solar
masses. We argue that the mass of the white dwarf is closer to 0.45 solar
masses, hence it appears that the white dwarf has a relatively large residual
hydrogen envelope. The mass of the M-star is then M_M = 0.28 +/- 0.05 solar
masses, and the inclination is i = 77 +/- 7 degrees. We discuss briefly how PG
1224+309 may be used to constrain theories of close binary star evolution, and
the past and future histories of PG 1224+309 itself. The star is both a
``post-common envelope'' star and a ``pre-cataclysmic binary'' star. Mass
transfer by Roche-lobe overflow should commence in about 10 Gyr.Comment: 17 pages, 8 figures, AAS LaTeX, to appear in AJ, March 199
Ethical Matrix Manual
The ethical matrix is a conceptual tool designed to help decision-makers (as individuals or working in groups) reach sound judgements or decisions about the ethical acceptability and/or optimal regulatory controls for existing or prospective technologies in the field of food and agriculture
Spectroscopy of Nine Cataclysmic Variable Stars
We present optical spectroscopy of nine cataclysmic binary stars, mostly
dwarf novae, obtained primarily to determine orbital periods Porb. The stars
and their periods are LX And, 0.1509743(5) d; CZ Aql, 0.2005(6) d; LU Cam,
0.1499686(4) d; GZ Cnc, 0.0881(4) d; V632 Cyg, 0.06377(8) d; V1006 Cyg,
0.09903(9) d; BF Eri, 0.2708804(4) d; BI Ori, 0.1915(5) d; and FO Per, for
which Porb is either 0.1467(4) or 0.1719(5) d.
Several of the stars proved to be especially interesting. In BF Eri, we
detect the absorption spectrum of a secondary star of spectral type K3 +- 1
subclass, which leads to a distance estimate of approximately 1 kpc. However,
BF Eri has a large proper motion (100 mas/yr), and we have a preliminary
parallax measurement that confirms the large proper motion and yields only an
upper limit for the parallax. BF Eri's space velocity is evidently large, and
it appears to belong to the halo population. In CZ Aql, the emission lines have
strong wings that move with large velocity amplitude, suggesting a
magnetically-channeled accretion flow. The orbital period of V1006 Cyg places
it squarely within the 2- to 3-hour "gap" in the distribution of cataclysmic
binary orbital periods.Comment: 31 pages, 5 postscript and one PNG figure. Accepted for PAS
'The language of the naked facts': Joseph Priestley on language and revealed religion
Joseph Priestley (1733-1804) is usually remembered for his experiments in natural
philosophy and celebrated for his isolation of the gas we now call oxygen. However,
Priestley had a wide range of interests and published extensively on education, history,
politics, political philosophy, language, theology and religion. He dedicated his life to
elucidating a coherent set of epistemological, metaphysical and theological principles
which he believed explained the human mind, the natural world and the nature of God
and revelation. Recent studies of Priestley have emphasised the difficulties that arise
from isolating the various aspects of his thought and the fruitful outcome of uncovering
the many connections between his diverse areas of study. With this in mind, the present
dissertation aims to elucidate the relationship between two aspects of Priestleyâs thought
that have not previously been studied together. It examines his theory of language and
argument alongside his work on theology and the evidences of revelation. Chapter One
provides an overview of Priestleyâs epistemology, focusing on his work on induction,
judgment and assent. Chapter Two looks at Priestleyâs analysis of the role of the
passions in our assent to propositions and the progressive generation of the personality,
while paying particular attention to the origins of figurative language. Chapter Three
examines Priestleyâs theory of language development including the relationship
between figurative language and the extension of vocabulary and the close connection
between language and culture. Chapter Four demonstrates that Priestleyâs discussion of
the evidences of revealed religion is structured around his theory of assent and
judgment. It also explains how assent to revelation is essential for the generation and
transcendence of the âselfâ. Chapter Five brings all the themes of the dissertation
together in a discussion of Priestleyâs rational theology and examines his analysis of
figurative language in scripture
CSS100603:112253-111037: A helium-rich dwarf nova with a 65 minute orbital period
We present time-resolved optical spectroscopy of the dwarf nova
CSS100603:112253-111037. Its optical spectrum is rich in helium, with broad,
double-peaked emission lines produced in an accretion disc. We measure a line
flux ratio HeI5876/H_alpha = 1.49 +/- 0.04, a much higher ratio than is
typically observed in dwarf novae. The orbital period, as derived from the
radial velocity of the line wings, is 65.233 +/- 0.015 minutes. In combination
with the previously measured superhump period, this implies an extreme mass
ratio of M_2/M_1 = 0.017 +/- 0.004. The H_alpha and HeI6678 emission lines
additionally have a narrow central spike, as is often seen in the spectra of AM
CVn type stars. Comparing its properties with CVs, AM CVn systems and hydrogen
binaries below the CV period minimum, we argue that CSS100603:112253-111037 is
the first compelling example of an AM CVn system forming via the evolved CV
channel.
With the addition of this system, evolved cataclysmic variables (CVs) now
account for seven per cent of all known semi-detached white dwarf binaries with
Porb < 76 min. Two recently discovered binaries may further increase this
figure. Although the selection bias of this sample is not yet well defined,
these systems support the evolved CV model as a possible formation channel for
ultracompact accreting binaries. The orbital periods of the three ultracompact
hydrogen accreting binaries overlap with those of the long period AM CVn stars,
but there are currently no known systems in the period range 67 - 76 minutes.Comment: 10 pages, 6 figures. Accepted for publication in MNRA
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