WIND VARIABILITY IN BZ CAMELOPARDALIS Honeycutt, R K; Kafka, S; Robertson, J W
The Astronomical journal,
02/2013, Letnik:
145, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Sequences of spectra of the nova-like cataclysmic variable (CV) BZ Cam were acquired on nine nights in 2005-2006 in order to study the time development of episodes of wind activity known to occur ...frequently in this star. We confirm the results of Ringwald & Naylor that the P-Cygni absorption components of the lines mostly evolve from higher expansion velocity to lower velocity as an episode progresses. We derive a new orbital ephemeris for BZ Cam, using the radial velocity of the core of the He I lambda5876 line, finding P = 0.15353(4). Using this period, the wind episodes in BZ Cam are found to be concentrated near the inferior conjunction of the emission line source. This result helps confirm that the winds in nova-like CVs are often phase dependent, in spite of the puzzling implication that such winds lack axisymmetry. We suggest that some flickering events lead to only back-side winds which will not have associated P-Cygni profiles.
We present long-term photometry of five magnetic cataclysmic variables (MCVs) that displayed pronounced VY Scl-like low states during the interval 1990-2004. A total of 43 transitions to and from the ...low states are analyzed and compared with the properties of disk VY Scl transitions from an earlier study. We find that the speeds and shapes of the transitions of both disk and magnetic systems above the CV period gap suggest that the low states are due to starspots on the secondary star drifting in front of the L1 point. For systems below the gap, the characteristics of the transitions point to X-ray irradiation on the L1 point for the cause of the low states. Our results are in accord with the nature of the secondary star, which is expected to be fully convective for systems below the gap. Finally, unresolved flaring events present in the low states of the MCVs in our sample are attributed to activity on the secondary, indicating that these secondaries are indeed chromospherically active.
We present new red/near-infrared spectra of the low-accretion-rate polar J204827.9+005008.9. Compared to 2004 spectra in the literature, our 2008 data show more structured emission-line profiles. All ...emission lines in our spectra have two components at most orbital phases. The stronger component has a sinusoidal velocity variation (K∼ 120 km s−1) and is likely due to irradiation of the inner hemisphere of the secondary star by the white dwarf. Based on the appearance of the Hα Doppler tomogram, the weaker, larger amplitude, line component likely originates in a ballistic stream from the L1 point. J2048 is thought to be accreting via a wind from the secondary star, so the detection of velocity features consistent with the velocities of Roche lobe overflow is unexpected. It appears that J2048 was experiencing an interval of enhanced mass transfer during our observations. We briefly discuss scenarios that might lead to such a situation, such as changes in the chromospheric activity level on the secondary star.
When accretion temporarily ceases in the polar AM Her, the emission-line profiles are known to develop several distinct components, whose origin remains poorly understood. The new low-state spectra ...reported here have a more favorable combination of spectral resolution, time resolution (image3 minute exposures), and S/N than earlier work, revealing additional details of the orbital dependence of the line profiles. The central strong feature of H alpha is found to be composed of two components of similar strength, one having image km s super(-1) and phased with the motion of the secondary star, the other having little or no detectable radial velocity variations. We attribute the central line component to gas near the coupling region, perhaps with a contribution from irradiation of the secondary star. The two satellite components have radial velocity offsets of image+/-250 km s super(-1) on either side of the central strong H alpha peak. These satellites most likely arise in large loops of magnetically confined gas near the secondary star due to magnetic activity on the donor star and/or interactions of the magnetic fields of the two stars. Doppler maps show that these two satellite features have concentrations at velocities that match the velocity locations of L4 and L5 in the system.
We find a dimming during optical quiescence of the cataclysmic variable WZ Sge by about half a magnitude between superoutbursts. We connect the dimming with the development of a cavity in the inner ...part of the accretion disk. We suggest that, when the cavity is big enough, accretion of material is governed by the magnetic field of the white dwarf and pulsations from the weakly magnetic white dwarf appear. The time scale of forming the cavity is about a decade, and it persists throughout the whole quiescent phase. Such a cavity can be accommodated well by the proposed magnetic propeller model for WZ Sge, where during quiescence mass is being expelled by the magnetic white dwarf from the inner regions of the accretion disk to larger radii.
FBS 0107-082 is an emission line object previously classified as a nova-like cataclysmic variable star. New optical spectroscopy shows very strong hydrogen Balmer lines, along with a nebular ...forbidden line spectrum and absorption features from an early-F photosphere. When combined with other IR and optical data from the literature, these data point to the object being a symbiotic nova seen in a prolonged outburst. Photometry on timescales of minutes, days, and years shows only very weak variability.
Spectroscopy of 222 late-type dwarfs in the Praesepe open cluster is used to measure the strengths of molecular and atomic features and to examine their sensitivity to chromospheric activity as ...measured by the strength of Ha emission. For this cluster we confirm the results of Hawley and coworkers that some TiO features are selectively weakened among active field stars. However, a similar effect for CaOH is only weakly confirmed. Using differential measures of the strengths of features with respect to the median in narrow color bins, we also find that absorption in the Ca II IR triplet is selectively weakened in more active stars, while absorption at K I and Na I is strengthened. A comparison of the distribution of the Ha strengths with V - I color in Praesepe and the similarly aged Hyades cluster indicates that the onset of M dwarf activity occurs at a significantly redder color in Praesepe than in the Hyades. Analysis of similar data on eight clusters from the literature is used to explore the relationship between age and activity in open clusters. We quantify the dependence on cluster age of the location along the main sequence for the onset of activity, confirming that the critical color at which activity becomes prominent is a nearly linear function of the logarithm of the age.
The 22 yr light curve of HR Lyr, acquired with a typical cadence of 2-6 days, is examined for periodic and quasi-periodic variations. No persistent periodicities are revealed. Rather, the light curve ...variations often take the form of nearly linear rises and falls having typical e-folding times of about 100 days. Occasional ~0.6 mag outbursts are also seen, with properties similar to those of small outbursts found in some nova-like cataclysmic variables. When the photometry is formed into yearly averages, a decline of 0.012 + or - 0.005 mag yr super(-1) is apparent, consistent with the fading of irradiation-induced M following the nova. The equivalent width of H alpha is tabulated at three epochs over the interval 1986-2008 in order to compare with a recent result for DK Lac in which H alpha was found to be fading 50 yr after the nova. However, our results for such a fading in HR Lyr are inconclusive.
We report on extensive photometry of DK Lac obtained during the interval 1990-2009, which includes a 2 mag low state during 2001-2003. Much of the photometry consists of exposures obtained with a ...typical spacing of several days, but also includes 26 sequences of continuous photometry each lasting 2-7 hr. We find no evidence for periodicities in our data. We do find that the random variations in the low state are approximately twice those in the high state, when expressed in magnitudes. The lack of orbital-timescale variations is attributed to the nearly face-on presentation of the disk. There is a 0.2 mag decline in the high-state brightness of the system over 19 years, which is consistent with the behavior of other old novae in the decades following outburst. High-state spectra are also presented and discussed. We find that the equivalent width of H Delta *a falls by about double from 1991 to 2008. The photometric properties are discussed in the context of the hibernation scenario for the behavior of novae between outbursts, in which we conclude that low states in old novae are probably unrelated to their possible entrance into hibernation.
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