78 research outputs found
Radial Velocity Studies of Close Binary Stars.VII. Methods and Uncertainties
Methods used in the radial-velocity program of short-period binary systems at
the David Dunlap Observatory are described with particular stress on the
Broadening Function (BF) formalism. This formalism has permitted determination
of radial velocities from complex spectra of multiple-component systems with
component stars showing very different degree of rotational line broadening.
The statistics of random errors of orbital parameters is discussed on the basis
of the available orbital solutions presented in the six previous papers of the
series, each with ten orbits. The difficult matter of systematic uncertainties
in orbital parameters is illustrated for one typical case of GM Dra from the
most recent Paper VI.Comment: AASTeX5, 5 figures, extensively modified after the AJ revie
Book No. 44 Krzepnięcie Metali i Stopów
SUMMARY The numerical solution of 2D Stefan problem is discussed. The Stefan model describes the solidification of pure metals or eutectic alloys in macro scale. From the numerical view point the solution of this task is very complex, in particular, for 2D or 3D domains. In literature one can find the algorithms basing on the substitution of the Stefan model by the artificial mushy zone one. Such approach is also presented in this paper
Radial Velocity Studies of Close Binary Stars. XI
Radial-velocity measurements and sine-curve fits to the orbital radial
velocity variations are presented for ten close binary systems: DU Boo, ET Boo,
TX Cnc, V1073 Cyg, HL Dra, AK Her, VW LMi, V566 Oph, TV UMi and AG Vir. By this
contribution, the DDO program has reached the point of 100 published radial
velocity orbits. The radial velocities have been determined using an improved
fitting technique which uses rotational profiles to approximate individual
peaks in broadening functions.
Three systems, ET Boo, VW LMi and TV UMi, were found to be quadruple while AG
Vir appears to be a spectroscopic triple. ET Boo, a member of a close visual
binary with years, was previously known to be a multiple
system, but we show that the second component is actually a close,
non-eclipsing binary. The new observations enabled us to determine the
spectroscopic orbits of the companion, non-eclipsing pairs in ET Boo and VW
LMi. The particularly interesting case is VW LMi, where the period of the
mutual revolution of the two spectroscopic binaries is only 355 days.
While most of the studied eclipsing pairs are contact binaries, ET Boo is
composed of two double-lined detached binaries and HL Dra is single-lined
detached or semi-detached system. Five systems of this group were observed
spectroscopically before: TX Cnc, V1073 Cyg, AK Her (as a single-lined binary),
V566 Oph, AG Vir, but our new data are of much higher quality than the previous
studies.Comment: Accepted by AJ, August 2006, 10 figures, 3 table
The photometric-amplitude and mass-ratio distributions of contact binary stars
The distribution of the light-variation amplitudes, A(a), in addition to
determining the number of undiscovered contact binary systems falling below
photometric detection thresholds and thus lost to statistics, can serve as a
tool in determination of the mass-ratio distribution, Q(q), which is very
important for understanding of the evolution of contact binaries. Calculations
of the expected A(a) show that it tends to converge to a mass-ratio dependent
constant value for a->0. Strong dependence of A(a) on Q(q) can be used to
determine the latter distribution, but the technique is limited by the presence
of unresolved visual companions and by blending in crowded areas of the sky.
The bright-star sample to 7.5 magnitude is too small for an application of the
technique while the the Baade's Window sample from the OGLE project may suffer
stronger blending; thus the present results are preliminary and illustrative
only. Estimates based on the Baade's Window data from the OGLE project, for
amplitudes a>0.3 mag. where the statistics appear to be complete allowing
determination of Q(q) over 0.12<q<1, suggest a steep increase of Q(q) with
q->0. The mass-ratio distribution can be approximated by a power law, either
Q(q)~(1-q)^a1 with a1=6+/-2 or Q(q)~q^b1, with b1=-2+/-0.5, with a slight
preference for the former form. Both forms must be modified by the
theoretically expected cut-off caused by a tidal instability at about q_min
0.07-0.1. An expected maximum in Q(q), is expected to be mapped into a local
maximum in A(a) around 0.2-0.25 mag.Comment: AASTeX5, 12 figures, 5 tables, accepted by AJ, Aug.200
The Peculiar Type Ia Supernova 1999by: Spectroscopy at Early Epochs
We present medium resolution (lambda/Delta lambda = 2500) optical
spectroscopy of SN 1999by in NGC 2841 made around its light maximum. The depth
ratio of the two Si II features at 5800 AA and 6150 AA being R(SiII) approx.
0.63 at maximum indicates that this SN belongs to the peculiar, sub-luminous
SNe Ia. Radial velocities inferred from the minimum of the 6150 AA trough
reveal a steeper decline of the velocity curve than expected for ``normal'' SNe
Ia, consistent with the behavior of published VRI light curves. A revised
absolute magnitude of SN 1999by and distance to its host galaxy NGC 2841 is
estimated based on the Multi-Color Light Curve Shape (MLCS) method, resulting
in M_V(max)=-18.06+/- 0.1 mag and d = 17.1+/-1.2 Mpc, respectively. An
approximative linear dependence of the luminosity parameter Delta on R(SiII) is
presented.Comment: accepted for publication in Astron. Journal (2001 June
Time-Series Photometry of M67: W UMa Systems, Blue Stragglers, and Related Systems
We present an analysis of over 2200 V images taken on 14 nights at the Mt.
Laguna 1 m telescope of the open cluster M67. Our observations overlap but
extend beyond the field analyzed by Gilliland et al. (1991), and complement
data recently published by van den Berg et al. (2002) and Stassun et al.
(2002). We show variability in the light curves of all 4 of the known W UMa
variables on timescales ranging from a day to decades (for AH Cnc). We have
modeled the light curve of AH Cnc, and the total eclipses allow us to determine
q = 0.16 +0.03/-0.02 and i = 86 +4/-8 degrees. The position of this system near
the turnoff of M67 makes it useful for constraining the turnoff mass for the
cluster. We have also detected two unusual features in the light curve of AH
Cnc that may be caused by prominences. We have also monitored cluster blue
stragglers for variability, and we present evidence hinting at low level
variations in the stragglers S752, S968, and S1263, and we place limits on the
variability of a number of other cluster blue stragglers. Finally, we provide
photometry of the sub-subgiant branch star S1063 showing variability on
timescales similar to the orbital period, while the ``red straggler'' S1040
shows evidence of an unexplained drop in brightness at phases corresponding to
the passage of the white dwarf in front of the giant.Comment: 44 pages, 16 figures, AASTeX, accepted for A
Time Series Photometry of Variable Stars in the Globular Cluster NGC 6397
Time series BVI photometry is presented for 16 short-period variables located
in the central region of the globular cluster NGC 6397. The sample includes 9
newly detected variables. The light curve of cataclysmic variable CV6 shows
variability with a period of 0.2356 days. We confirm an earlier reported period
of 0.472 days for cataclysmic variable CV1. Phased light curves of both CVs
exhibit sine-like light curves, with two minima occurring during each orbital
cycle. The secondary component of CV1 has a low average density of 0.83
g/cm^{3} indicating that it cannot be a normal main sequence star. Variables
among the cluster blue stragglers include a likely detached eclipsing binary
with orbital period of 0.787 days, three new SX Phe stars (one of which has the
extremely short period of 0.0215 days), and three low amplitude variables which
are possible gamma Doradus variables.Comment: 28 pages, 13 figure
Massive pulsating stars observed by BRITE-Constellation. I. The triple system Beta Centauri (Agena)
This paper aims to precisely determine the masses and detect pulsation modes
in the two massive components of Beta Cen with BRITE-Constellation photometry.
In addition, seismic models for the components are considered and the effects
of fast rotation are discussed. This is done to test the limitations of seismic
modeling for this very difficult case. A simultaneous fit of visual and
spectroscopic orbits is used to self-consistently derive the orbital
parameters, and subsequently the masses, of the components. The derived masses
are equal to 12.02 +/- 0.13 and 10.58 +/- 0.18 M_Sun. The parameters of the
wider, A - B system, presently approaching periastron passage, are constrained.
Analysis of the combined blue- and red-filter BRITE-Constellation photometric
data of the system revealed the presence of 19 periodic terms, of which eight
are likely g modes, nine are p modes, and the remaining two are combination
terms. It cannot be excluded that one or two low-frequency terms are rotational
frequencies. It is possible that both components of Beta Cen are Beta Cep/SPB
hybrids. An attempt to use the apparent changes of frequency to distinguish
which modes originate in which component did not succeed, but there is
potential for using this method when more BRITE data become available. Agena
seems to be one of very few rapidly rotating massive objects with rich p- and
g-mode spectra, and precisely known masses. It can therefore be used to gain a
better understanding of the excitation of pulsations in relatively rapidly
rotating stars and their seismic modeling. Finally, this case illustrates the
potential of BRITE-Constellation data for the detection of rich-frequency
spectra of small-amplitude modes in massive pulsating stars.Comment: 17 pages (with Appendix), 15 figures, accepted for publication in A&
A Spectroscopic Survey of a Sample of Active M Dwarfs
A moderate resolution spectroscopic survey of Fleming's sample of 54 X-ray
selected M dwarfs with photometric distances less than 25 pc is presented.
Radial and rotation velocities have been measured by fits to the H-alpha
profiles. Radial velocities have been measured by cross correlation. Artificial
broadening of an observed spectrum has produced a relationship between H-alpha
FWHM and rotation speed, which we use to infer rotation speeds for the entire
sample by measurement of the H-alpha emission line. We find 3 ultra-fast
rotators (UFRs, vsini > 100km/s), and 8 stars with 30 < vsini < 100 km/s. The
UFRs have variable emission. Cross-correlation velocities measured for
ultra-fast rotators (UFRs) are shown to depend on rotation speed and the
filtering used. The radial velocity dispersion of the sample is 17 km/s. A new
double emission line spectroscopic binary with a period of 3.55 days has been
discovered, and another known one is in the sample. Three other objects are
suspected spectroscopic binaries, and at least six are visual doubles. The only
star in the sample observed to have significant lithium is a known TW Hya
Association member, TWA 8A. These results show that there are a number of young
(< 10^8 yr) and very young (< 10^7 yr) low mass stars in the immediate solar
neighbourhood. The H-alpha activity strength does not depend on rotation speed.
Our fast rotators are less luminous than similarly fast rotators in the
Pleiades. They are either younger than the Pleiades, or gained angular momentum
in a different way.Comment: 38 pages incl. 14 figures and 4 tables, plus 12 pages of table for
electronic journal only; LaTeX, aastex.cls. Accepted 07/18/02 for publication
in The Astronomical Journa
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