48 research outputs found
A multichannel fiber optic photometer present performance and future developments
A three channel photometer for simultaneous multicolor observations was designed with the aim of making possible highly efficient photometry of fast variable objects like cataclysmic variables. Experiences with this instrument over a period of three years are presented. Aspects of the special techniques applied are discussed with respect to high precision photometry. In particular, the use of fiber optics is critically analyzed. Finally, the development of a new photometer concept is discussed
High-speed, energy-resolved, STJ observations of the AM Her system V2301 Oph
We present high time-resolution optical energy-resolved photometry of the
eclipsing cataclysmic variable V2301 Oph made using the ESA S-Cam detector, an
array of photon counting super-conducting tunnel junction (STJ) devices with
intrinsic energy resolution. Three eclipses were observed, revealing
considerable variation in the eclipse shape, particularly during ingress. The
eclipse shape is shown to be understood in terms of AM Her accretion via a
bright stream, with very little contribution from the white dwarf photosphere
and/or hotspot. About two thirds of the eclipsed light arises in the threading
region. Variation in the extent of the threading region can account for most of
the variations observed between cycles. Spectral fits to the data reveal a
10,000K blackbody continuum with strong, time-varying emission lines of
hydrogen and helium. This is the first time that stellar emission lines have
been detected in the optical band using a non-dispersive photon-counting
system.Comment: Accepted A&
Time-Resolved HST Spectroscopy of Four Eclipsing Magnetic Cataclysmic Variables
Time-resolved HST UV eclipse spectrophotometry is presented for the magnetic
CVs V1309 Ori, MN Hya, V2301 Oph, and V1432 Aql. Separation of the light curves
into wavebands allows the multiple emission components to be distinguished.
Photospheric hot spots are detected in V1309 Ori and V2301 Oph. The emission-
line spectra of V1309 Ori and MN Hya are unusual, with the strength of N V 1240
and N IV 1718 suggesting an overabundance of nitrogen. Three epochs of
observation of the asynchronous V1432 Aql cover ~1/3 of a 50-day lap cycle
between the white dwarf spin and binary orbit. The light curves vary from epoch
to epoch and as a function of waveband. The dereddened UV spectrum is extremely
bright and the spectral energy distribution coupled with the duration of
eclipse ingress indicate that the dominant source of energy is a hot
(T~35,000K) white dwarf. Undiminished line emission through eclipse indicates
that the eclipse is caused by the accretion stream, not the secondary star. The
hot white dwarf, combined with its current asynchronous nature and rapid
timescale for relocking, suggests that V1432 Aql underwent a nova eruption in
the past 75-150 yr. The reversed sense of asynchronism, with the primary star
currently spinning up toward synchronism, is not necessarily at odds with this
scenario, if the rotation of the magnetic white dwarf can couple to the ejecta
during the wind phase of the eruption.Comment: To appear in ApJ Part 1; 25 pages, 12 figure
IP Pegasi: Investigation of the accretion disk structure. Searching evidences for spiral shocks in the quiescent accretion disk
We present the results of spectral investigations of the cataclysmic variable
IP Peg in quiescence. Optical spectra obtained on the 6-m telescope at the
Special Astrophysical Observatory (Russia), and on the 3.5-m telescope at the
German-Spanish Astronomical Center (Calar Alto, Spain), have been analysed by
means of Doppler tomography and Phase Modelling Technique. From this analysis
we conclude that the quiescent accretion disk of IP Peg has a complex
structure. There are also explicit indications of spiral shocks. The Doppler
maps and the variations of the peak separation of the emission lines confirm
this interpretation. We have detected that all the emission lines show a rather
considerable asymmetry of their wings varying with time. The wing asymmetry
shows quasi-periodic modulations with a period much shorter than the orbital
one. This indicates the presence of an emission source in the binary rotating
asynchronously with the binary system. We also have found that the brightness
of the bright spot changes considerably during one orbital period. The spot
becomes brightest at an inferior conjunction, whereas it is almost invisible
when it is located on the distant half of the accretion disk. Probably, this
phenomenon is due to an anisotropic radiation of the bright spot and an eclipse
of the bright spot by the outer edge of the accretion disk.Comment: 13 pages, 11 figures (= 21 EPS files), accepted for publication in
A&
Dwarf Nova Oscillations and Quasi-Periodic Oscillations in Cataclysmic Variables: III. A New Kind of Dwarf Nova Oscillation, and Further Examples of the Similarities to X-Ray Binaries
We present measurements of the periods of Dwarf Nova Oscillations (DNOs) and
Quasi-Periodic Oscillations (QPOs) in Cataclysmic Variable stars (CVs), many
culled from published literature, but also others newly observed (in VZ Pyx, CR
Boo, OY Car, Z Cha, AQ Eri, TU Men, HX Peg, CN Ori, V893 Sco, WX Hyi and
EC2117-54). These provide data for 26 systems. We show that in general P_QPO ~
15 P_DNO and that the correlation for CVs extends by three orders of magnitude
lower in frequency the similar relationship found for X-Ray binaries. In
addition, we have found that there is a second type of DNO, previously
overlooked, which have periods ~ 4 times those of the regular DNOs (As well as
those mined from publications, we have observed them in VW Hyi, OY Car, AQ Eri,
V803 Cen, CR Boo, VZ Pyx, HX Peg and EC2117-54). Often both types of DNO
coexist. Unlike the standard DNOs, the periods of the new type, which we refer
to as longer period DNOs (lpDNOs), are relatively insensitive to accretion
luminosity and can even appear in quiescence of dwarf novae. We interpret them
as magnetically channelled accretion onto the differentially rotating main body
of the white dwarf primary, rather than onto a rapidly slipping equatorial belt
as in the case of the standard DNOs. This is supported by published
measurements of v sin(i) for some of the primaries. Some similarities of the
DNOs, lpDNOs and QPOs in CVs to the three types of QPO in X-Ray binaries (burst
pulsation, high and low frequency QPOs) are noted.Comment: 19 pages, 30 figures. To appear in MNRA
Pulsations, Boundary Layers, and Period Bounce in the Cataclysmic Variable RE J1255+266
We report time-series photometry of the quiescent optical counterpart of the
EUV transient RE J1255+266. The star appears as a DA white dwarf with bright
emission lines and a complex spectrum of periodic signals in its light curve. A
signal at 0.0829 d is likely to be the orbital period of the underlying
cataclysmic binary (probably a dwarf nova). Characteristic periods of 1344,
1236, and 668 s are seen, and a host of weaker signals. We interpret these
noncommensurate signals as (nonradial) pulsation periods of the white dwarf.
The donor star is unseen at all wavelengths, and the accretion rate is very
low. We estimate a distance of 180+-50 pc, and M_v=14.6+-1.3 for the accretion
light. The binary probably represents a very late stage of evolution, with the
donor star whittled down to M_2<0.05 M_sol. Such binaries stubbornly resist
discovery due to their faintness and reluctance to erupt, but are probably a
very common type of cataclysmic variable. If the signal at 0.0829 d is indeed
the orbital period, then the binary is an excellent candidate as a "period
bouncer". Plausible colleagues in this club include four dwarf novae and the
(so far) noneruptive stars GD 552 and 1RXS J105010.3-140431 (hereafter RX
1050).
The 1994 EUV eruption implies a soft X-ray/EUV luminosity of 10^(34-35)
erg/s, greater than that of any other dwarf nova. We attribute that to a
favorable blend of properties: a high-mass white dwarf; a very transparent line
of sight (the "Local Chimney"); and a low binary inclination. The first
maximizes the expected temperature and luminosity of boundary-layer emission;
the other two increase the likelihood that soft X-rays can survive their
perilous passage through an accretion-disk wind and the interstellar medium.Comment: PDF, 43 pages, 5 tables, 10 figures, 1 appendix; accepted, in press,
to appear May 2005, PASP; more info at http://cba.phys.columbia.edu
Superhumps in Cataclysmic Binaries. XXIV. Twenty More Dwarf Novae
We report precise measures of the orbital and superhump period in twenty more
dwarf novae. For ten stars, we report new and confirmed spectroscopic periods -
signifying the orbital period P_o - as well as the superhump period P_sh. These
are GX Cas, HO Del, HS Vir, BC UMa, RZ Leo, KV Dra, KS UMa, TU Crt, QW Ser, and
RZ Sge. For the remaining ten, we report a medley of P_o and P_sh measurements
from photometry; most are new, with some confirmations of previous values.
These are KV And, LL And, WX Cet, MM Hya, AO Oct, V2051 Oph, NY Ser, KK Tel, HV
Vir, and RX J1155.4-5641.
Periods, as usual, can be measured to high accuracy, and these are of special
interest since they carry dynamical information about the binary. We still have
not quite learned how to read the music, but a few things are clear. The
fractional superhump excess epsilon [=(P_sh-P_o)/P_o] varies smoothly with P_o.
The scatter of the points about that smooth curve is quite low, and can be used
to limit the intrinsic scatter in M_1, the white dwarf mass, and the
mass-radius relation of the secondary. The dispersion in M_1 does not exceed
24%, and the secondary-star radii scatter by no more than 11% from a fixed
mass-radius relation. For the well-behaved part of epsilon(P_o) space, we
estimate from superhump theory that the secondaries are 18+-6% larger than
theoretical ZAMS stars. This affects some other testable predictions about the
secondaries: at a fixed P_o, it suggests that the secondaries are (compared
with ZAMS predictions) 40+-14% less massive, 12+-4% smaller, 19+-6% cooler, and
less luminous by a factor 2.5(7). The presence of a well-defined mass-radius
relation, reflected in a well-defined epsilon(P_o) relation, strongly limits
effects of nuclear evolution in the secondaries.Comment: PDF, 62 pages, 7 tables, 21 figures; accepted, in press, to appear
November 2003, PASP; more info at http://cba.phys.columbia.edu
The underluminous Type Ia Supernova 2005bl and the class of objects similar to SN 1991bg
Optical observations of the Type Ia supernova (SN Ia) 2005bl in NGC 4070,
obtained from -6 to +66 d with respect to the B-band maximum, are presented.
The photometric evolution is characterised by rapidly-declining light curves
and red colours at peak and soon thereafter. With M_B,max = -17.24 the SN is an
underluminous SN Ia, similar to the peculiar SNe 1991bg and 1999by. This
similarity also holds for the spectroscopic appearance, the only remarkable
difference being the likely presence of carbon in pre-maximum spectra of SN
2005bl. A comparison study among underluminous SNe Ia is performed, based on a
number of spectrophotometric parameters. Previously reported correlations of
the light-curve decline rate with peak luminosity and R(Si) are confirmed, and
a large range of post-maximum Si II lambda6355 velocity gradients is
encountered. 1D synthetic spectra for SN 2005bl are presented, which confirm
the presence of carbon and suggest an overall low burning efficiency with a
significant amount of leftover unburned material. Also, the Fe content in
pre-maximum spectra is very low, which may point to a low metallicity of the
precursor. Implications for possible progenitor scenarios of underluminous SNe
Ia are briefly discussed.Comment: 24 pages, 24 figures, accepted for publication in MNRA