Stefan W. Mochnacki

Radial Velocity Studies of Close Binary Stars. III

Radial velocity measurements and simple sine-curve fits to the orbital velocity variations are presented for the third set of 10 close binary systems: CN And, HV Aqr, AO Cam, YY CrB, FU Dra, RZ Dra, UX Eri, RT LMi, V753 Mon, and OU Ser. All systems except two (CN And and RZ Dra) are contact, double-line spectroscopic binaries, with four of them (YY CrB, FU Dra, V753 Mon, and OU Ser) being the recent discoveries of the Hipparcos satellite project. The most interesting object is V753 Mon with the mass ratio closest to unity among all contact systems (q = 0.970 ± 0.003) and large total mass [(M1 + M2) sin3 i = 2.93 ± 0.06]. Several of the studied systems are prime candidates for combined light and radial velocity synthesis solutions.

Radial Velocity Studies of Close Binary Stars. VIII.

Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for the seventh set of 10 close binary systems: V410 Aur, V523 Cas, QW Gem, V921 Her, V2357 Oph, V1130 Tau, HN UMa, HX UMa, HD 93917, and NSV 223. All systems but three (V523 Cas, HD 93917, NSV 223) were discovered photometrically by the Hipparcos mission. All systems are double-lined (SB2) binaries, and all but the detached, very close system V1130 Tau are contact binaries. The broadening function permitted improvement of the orbital elements for V523 Cas, which was the only system observed before for radial velocity variations. Spectroscopic/visual companions were detected for V410 Aur and HX UMa. Several of the studied systems are prime candidates for combined light and radial velocity synthesis solutions.

Radial Velocity Studies of Close Binary Stars. V.

Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for the fifth set of 10 close binary systems: V376 And, EL Aqr, EF Boo, DN Cam, FN Cam, V776 Cas, SX Crv, V351 Peg, EQ Tau, and KZ Vir. All systems are double-lined, spectroscopic contact binaries (KZ Vir may be a low-inclination, close, noncontact binary), with seven (all except EL Aqr, SX Crv, and EQ Tau) being the recent photometric discoveries of the Hipparcos project. The most interesting object is SX Crv, a contact system with an unprecedented low mass ratio, q = 0.066 ± 0.003, whose existence challenges the current theory of tidal stability of contact systems. Several of the studied systems are prime candidates for combined light and radial velocity synthesis solutions.

Radial Velocity Studies of Close Binary Stars. VI.

Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for the sixth set of 10 close binary systems: SV Cam, EE Cet, KR Com, V410 Cyg, GM Dra, V972 Her, ET Leo, FS Leo, V2388 Oph, and II UMa. All systems except FS Leo are double-lined spectroscopic binaries. The type of FS Leo is unknown, while SV Cam is a close, detached binary; all remaining systems are contact binaries. Eight binaries (all except SV Cam and V401 Cyg) are the recent photometric discoveries of the Hipparcos satellite project. Five systems, EE Cet, KR Com, V401 Cyg, V2388 Oph, and II UMa, are members of visual/spectroscopic triple systems. We were able to observe EE Cet separately from its companion, but in the remaining four triple systems we could separate the spectral components only through the use of the broadening-function approach. Several of the studied systems are prime candidates for combined light and radial velocity synthesis solutions.

Evidence for Type Ia Supernova Diversity from Ultraviolet Observations with the Hubble Space Telescope

We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This data set provides unique spectral time series down to 2000 A. Significant diversity is seen in the near-maximum-light spectra (~2000-3500 A) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminosities measured in the uvw1/F250W filter are found to correlate with the B-band light-curve shape parameter Δm 15(B), but with much larger scatter relative to the correlation in the broadband B band (e.g., ~0.4 mag versus ~0.2 mag for those with 0.8 mag 3σ), being brighter than normal SNe Ia such as SN 2005cf by ~0.9 mag and ~2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects.

Doppler Imaging of VW Cephei: Distribution and Evolution of Starspots on a Contact Binary

We present maximum entropy Doppler images of the contact binary VW Cephei, produced from seven data sets of simultaneous spectroscopic and photometric data at epochs from 1991 March to 1993 May. The geometric and orbital parameters of the contact binary were fitted, along with third-light characteristics, at the same time as spots, using both the spectroscopic and photometric data to constrain the models. The Doppler images indicated the presence of large polar spots on both components. The polar spot on the primary was about 50° in diameter and slightly off-center, similar to polar spots on other unevolved systems, while the polar spot on the secondary was 30° in diameter. A number of lower latitude features were also present. Spots were found to migrate around the primary component in the same direction as the orbital motion of the system. Slow differential rotation of the primary component was observed, with spots at higher latitudes moving at higher angular rates. The spot distribution on the secondary appeared to be quite stable, with spots congregating at active longitudes, and with no organized pattern of migration. The spot coverage on both components was extremely high, though not unrealistic compared to spot coverages of some RS CVn systems. Spots covered 66% of the surface area of the primary and 55% of the secondary. The spot coverage was much greater than that suggested by asymmetry of the light curves. Our Doppler images were modeled in agreement with the Mullan starspot model. However, they also explained the success of the hot secondary model, since the bolometric flux-weighted mean surface temperature of the primary was less than that of the secondary, owing to the large numbers of nonblack spots. The models indicated the presence of a great number of unresolved spots. We discuss the implications of this to the field of Doppler imaging and argue in favor of the use of two-temperature photosphere models for the Doppler imaging of all rapidly rotating systems. We detected three flares at Hα and estimate that one such detectable flare occurs on VW Cep every 35 ± 20 hr. We also noted that the distribution of chromospheric emission at Hα over the primary of VW Cep may vary from epoch to epoch.

Radial Velocity Studies of Close Binary Stars. XI.

Radial-velocity measurements and sine-curve fits to orbital radial velocity variations are presented for 10 close binary systems: DU Boo, ET Boo, TX Cnc, V1073 Cyg, HL Dra, AK Her, VW LMi, V566 Oph, TV UMi, and AG Vir. With this contribution, the David Dunlap Observatory program has reached the point of 100 published radial velocity orbits. The radial velocities have been determined using an improved fitting technique that uses rotational profiles to approximate individual peaks in broadening functions. Three systems, ET Boo, VW LMi, and TV UMi, are found to be quadruple, while AG Vir appears to be a spectroscopic triple. ET Boo, a member of a close visual binary with Pvis = 113 yr, was previously known to be a multiple system, but we show that the second component is actually a close, noneclipsing binary. The new observations have enabled us to determine the spectroscopic orbits of the companion, noneclipsing pairs in ET Boo and VW LMi. A particularly interesting case is VW LMi, for which 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 a single-lined detached or semidetached system. Five systems of this group have been observed spectroscopically before: TX Cnc, V1073 Cyg, AK Her (as a single-lined binary), V566 Oph, and AG Vir, but our new data are of much higher quality than in the previous studies.

Radial Velocity Studies of Close Binary Stars. XIII

Radial velocity (RV) measurements and sine-curve fits to the orbital RV variations are presented for ten close binary systems: EG Cep, V1191 Cyg, V1003 Her, BD+7°3142, V357 Peg, V407 Peg, V1123 Tau, V1128 Tau, HH UMa, and PY Vir. While most of the studied eclipsing systems are contact binaries, EG Cep is a detached or a semidetached double-lined binary and V1003 Her is a close binary of an uncertain type seen at a very low inclination angle. We discovered two previously unknown triple systems, BD+7°3142 and PY Vir, both with late spectral-type (K2V) binaries. Of interest is the low mass-ratio (q = 0.106) close binary V1191 Cyg showing an extremely fast period increase; the system has a very short period for its spectral type and shows a W-type light curve, a feature rather unexpected for such a low mass-ratio system.

Radial Velocity Studies of Close Binary Stars. X.

Radial velocity measurements and sine-curve fits to orbital velocity variations are presented for the ninth set of 10 close binary systems: V395 And, HS Aqr, V449 Aur, FP Boo, SW Lac, KS Peg, IW Per, V592 Per, TU UMi, and FO Vir. The first three are very close, possibly detached, early-type binaries, and all three require further investigation. Particularly interesting is V395 And, whose spectral type is as early as B7/8 for a 0.685 day orbit binary. KS Peg and IW Per are single-line binaries, with the former probably hosting a very low mass star. We have detected a low-mass secondary in an important semidetached system, FO Vir, at q = 0.125 ± 0.005. The contact binary FP Boo is also a very small mass ratio system, q = 0.106 ± 0.005. The other contact binaries in this group are V592 Per, TU UMi, and the well-known SW Lac. V592 Per and TU UMi have bright tertiary companions; for these binaries, and for V395 And, we used a novel technique of arranging the broadening functions into a two-dimensional image in phase. The case of TU UMi turned out to be intractable even using this approach, and we have not been able to derive a firm radial velocity orbit for this binary. Three systems of this group were observed spectroscopically before: HS Aqr, SW Lac, and KS Peg.

Detection of Tertiary Components in W Ursae Majoris Systems

Extensive spectroscopic observations with good phase coverage of a small sample of W UMa systems were made at the David Dunlap Observatory. The data were found to be very sensitive to the presence of tertiary companions. All of the systems studied were found, or were previously known, to contain companion stars or binaries, including two systems not previously proven to have companions: SW Lac and V502 Oph. We suggest that the existence of tertiary components in W UMa systems is more widespread than previously known.