We describe two observations of the nova-like cataclysmic variable AC Cnc obtained with Kepler during its revamped second mission (K2). Using the K2 1 minute cadence mode, the data were obtained ...during campaigns 5 and 18. Campaign 5 (C05) lasted from ∼2015 April 27 to ∼2015 July 10, a total of 74.8 days, and yielded ∼106,000 measurements. Campaign 18 (C18) lasted from ∼2018 May 13 to ∼2018 July 2, a total of 50.7 days, yielding ∼72,000 measurements. The C05 light curve reveals two "stunted outbursts" having properties consistent with stunted bursts observed from the ground; a stunted burst was underway during the C18 observation when it ended. During a stunted outburst, the primary eclipse is found to increase in depth, but the residual brightness at the mid-primary eclipse remains nearly constant. By contrast, the secondary eclipse retains the same depth, but the brightness at the mid-secondary eclipse increases during outburst, following the orbital variations of the out-of-eclipse light. The eclipse ephemeris is statistically consistent with historical ephemerides and shows only marginal evidence for a period change. On the basis of the K2 data, we cannot confirm a previously reported non-orbital periodicity in AC Cnc.
212 M dwarfs in the Praesepe cluster have been monitored photometrically for three observing seasons. It is found that Praesepe M dwarfs earlier than ∼M4 often have significant photometric ...variations, while variability is not detected for >M4. Time series analysis was performed on 147 of the targets having likely variability in order to study possible periodicities. For 83% of these targets, we detected no periodicities; these null results included targets with published photometric periods from earlier work. Our detected periods ranged from 20 to 45 days, and we are not able to confirm any of the 1-5 day periods in Praesepe periods reported by Schultz et al., which we attribute to the very different observing cadences of the two studies. We conjecture that our more widely spaced data cannot adequately sample the Schultz et al. periodicities before the growth and decay of spots have a chance to ruin the coherence. The new periods we find in the range 20-45 days (in targets that do not overlap with those from Schultz having shorter periods) have very small false alarm probabilities. We argue that rotation is unlikely to be responsible for these 20-45 day periods. Perhaps short activity cycles in the Praesepe M dwarfs play a role in generating such periodicities.
Multiple and ancient origins of the domestic dog Vilà, Carles; Savolainen, Peter; Maldonado, Jesús E. ...
Science (American Association for the Advancement of Science),
06/1997, Letnik:
276, Številka:
5319
Journal Article
Recenzirano
Mitochondrial DNA control region sequences were analyzed from 162 wolves at 27 localities worldwide and from 140 domestic dogs representing 67 breeds. Sequences from both dogs and wolves showed ...considerable diversity and supported the hypothesis that wolves were the ancestors of dogs. Most dog sequences belonged to a divergent monophyletic clade sharing no sequences with wolves. The sequence divergence within this clade suggested that dogs originated more than 100,000 years before the present. Associations of dog haplotypes with other wolf lineages indicated episodes of admixture between wolves and dogs. Repeated genetic exchange between dog and wolf populations may have been an important source of variation for artificial selection.
Stunted outbursts are ∼0 6 eruptions, typically lasting 5-10 days, which are found in some novalike cataclysmic variables, including UU Aqr. The mechanism responsible for stunted outbursts is ...uncertain but is likely related to an accretion disk instability or to variations in the mass transfer rate. A campaign to monitor the eclipse light curves in UU Aqr has been conducted in order to detect any light curve distortions due to the appearance of a hot spot on the disk at the location of the impact point of the accretion stream. If stunted outbursts are due to a temporary mass transfer enhancement, then predictable deformations of the orbital light curve are expected to occur during such outbursts. This study used 156 eclipses on 135 nights during the years 2000-2012. During this interval, random samples found the system to be in stunted outbursts 4%-5% of the time, yielding ∼7 eclipses obtained during some stage of stunted outburst. About half of the eclipses obtained during stunted outbursts showed clear evidence for hot spot enhancement, providing strong evidence that the stunted outbursts in UU Aqr are associated with mass transfer variations. The other half of the eclipses during stunted outburst showed little or no evidence for hot spot enhancement. Furthermore, there were no systematic changes in the hot spot signature as stunted outbursts progressed. Therefore, we have tentatively attributed the changes in hot spot visibility during stunted outburst to random blobby accretion, which likely further modulates the strength of the accretion stream on orbital timescales.
Pre-outburst and post-outburst light curves and post-outburst eclipse timings are analyzed to measure any period (P) change related to nova Cl Aql's outburst of early 2000 and a mean post-outburst ...dP/dt, which then lead to estimates of the accreting component's rate of mass (M) change and its overall outburst-related change of mass over roughly a decade of observations. We apply a recently developed procedure for unified analysis of three timing-related data types (light curves, radial velocities, and eclipse timings), although with only light curves and timings in this case. Fits to the data are reasonably good without need for a disk in the light-curve model, although the disk certainly exists and has an important role in our post-outburst mass flow computations. Initial experiments showed that, although there seems to be an accretion hot spot, it has essentially no effect on derived outburst-related Delta P or on post-outburst dP/dt. Use of atomic time (HIED) in place of HID also has essentially nil effect on Delta P and dP/dt. We find Delta P consistently negative in various types of solutions, although at best only marginally significant statistically in any one experiment. Pre-outburst HJD sub(0) and P results are given, as are post-outburst HJD sub(0), P, and dP/dt, with light curves and eclipse times as joint input, and also with only eclipse time input. Post-outburst dP/dt is negative at about 2.4sigma. Explicit formulae for mass transfer rates and epoch-to-epoch mass change are developed and applied. A known offset in the magnitude zero point for 1991-1994 is corrected.
QU Carinae: Type Ia supernova in the making? Kafka, S; Honeycutt, R. K; Williams, R
Monthly notices of the Royal Astronomical Society,
11 September 2012, Letnik:
425, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
Variable Na i absorption lines have been reported in a number of Type Ia supernovae (SNeIa). The presence of this circumstellar material suggests that cataclysmic variables (CVs) with a ...giant donor star may be the progenitors of these SNeIa. We present echelle spectra of the CV QU Carinae which strengthen the connection between CVs of the V Sge class, the accretion wind evolution scenario, variable wind features, variable Na i absorption and SNeIa. This thread not only provides insight into the spectral peculiarities of QU Car, but also links SNeIa as a class with their parent systems.
V446 Her is the best example of an old nova which has developed dwarf nova (DN) eruptions in the post-nova state. We report on observed properties of the long-term light curve of V446 Her, using ...photometry over 19 years. Yearly averages of the outburst (OB) magnitudes show a decline of ~0.013 mag yr--1, consistent with the decline of other post-novae that do not have DN OBs. Previous suggestions of bimodal distributions of the amplitudes and widths of the OBs are confirmed. The OBs occur at a mean spacing of 18 days but the range of spacings is large (13-30 days). From simulations of DN OBs, it has been predicted that the OB spacing in V446 Her will increase as from the red dwarf companion slowly falls following the nova; however, the large intrinsic scatter in the spacings serves to hide any evidence of this effect. We do find a systematic change in the OB pattern in which the brighter, wider type of OBs disappeared after late 2003, and this phenomenon is suggested to be due to falling following the nova.
The 1990-2012 light curve of the nova-like (NL) cataclysmic variable V794 Aql is studied in order to characterize and better understand the transitions to and from the faint state, and the variations ...within the bright state. Investigations of earlier portions of this data had concluded that the transitions to the low state were much slower than the rapid recovery, giving a sawtoothed appearance to the light curve. This behavior differs from that of most other VY Scl stars, which led to an interpretation of the large amplitude sawtooths as being due to an accretion disk (AD) instability. However, more recent photometry strongly suggests that the bright state itself has transitions of 1-1.5 mag, and that earlier studies had intermixed these bright state variations with the transitions to the low state. These newly recognized variations within the bright state sometimes appear as small outbursts (OBs) with typical amplitudes of 0.5-1.5 mag and spacings of ~15-50 days. The rise times of the OBs are 2-3 times faster than the decline times. We argue that the V794 Aql bright state variations are due to AD behavior similar to that seen in dwarf novae, but with varying degrees of stability. Similar regular small OBs have also been reported in other NL CVs, which we compare with V794 Aql. The true deep low states in V794 Aql appear to be normal, having transition speeds and shapes very similar to the transitions in other VY Scl stars.
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