Predicting the Future of Superhumps in Classical Nova Systems

Oscillations observed in the light curve of Nova V1974 Cygni 1992 since summer 1994 have been interpreted as permanent superhumps. From simple calculations based on the Tidal-Disk Instability model of Osaki, and assuming that the accretion disc is the dominant optical source in the binary system, we predict that the nova will evolve to become an SU UMa system as its brightness declines from its present luminosity by another 2-3 magnitudes. Linear extrapolation of its current rate of fading (in magnitude units) puts the time of this phase transition within the next 2-4 years. Alternatively, the brightness decline will stop before the nova reaches that level, and the system will continue to show permanent superhumps in its light curve. It will then be similar to two other old novae, V603 Aql and CP Pup, that still display the permanent superhumps phenomenon 79 and 55 years, respectively, after their eruptions. We suggest that non-magnetic novae with short orbital periods could be progenitors of permanent superhump systems.Comment: 5 pages, 2 eps. figures, Latex, accepted for publication in MNRA

Nova V1425 Aquilae 1995 - The Early Appearance of Accretion Processes in An Intermediate Polar Candidate

Continuous CCD photometry of Nova Aquilae 1995 was performed through the standard B,V,R and I filters during three nights in 1995 and with the I filter during 18 nights in 1996. The power spectrum of the 1996 data reveals three periodicities in the light curve: 0.2558 d, 0.06005 d and 0.079 d, with peak-to-peak amplitudes of about 0.012, 0.014 and 0.007 mag. respectively. The two shorter periods are absent from the power spectrum of the 1995 light curve, while the long one is probably already present in the light curve of that year. We propose that V1425 Aql should be classified as an Intermediate - Polar CV. Accordingly the three periods are interpreted as the orbital period of the underlying binary system, the spin period of the magnetic white dwarf and the beat period between them. Our results suggest that no later than 15 months after the outburst of the nova, accretion processes are taking place in this stellar system. Matter is being transferred from the cool component, most likely through an accretion disc and via accretion columns on to the magnetic poles of the hot component.Comment: 7 pages, 4 eps. figures, Latex, accepted for publication in MNRA

A New Interpretation for the Second Peak of T Coronae Borealis Outbursts: A Tilting Disk around a Very Massive White Dwarf

A new interpretation for the second peak of T Coronae Borealis (T CrB) outbursts is proposed based on a thermonuclear runaway (TNR) model. The system consists of a very massive white dwarf (WD) with a tilting accretion disk and a lobe-filling red-giant. The first peak of the visual light curve of T CrB outbursts is well reproduced by the TNR model on a WD close to the Chandrasekhar mass ($M_{\rm WD} \gtrsim 1.35 ~M_\odot$), while the second peak is reproduced by the combination of the irradiated M-giant and the irradiated tilting disk. The derived fitting parameters are the WD mass $M_{\rm WD} \sim 1.35 ~M_\odot$, the M-giant companion mass $M_{\rm RG} \sim 0.7 M_\odot$ ($0.6-1.0 M_\odot$ is acceptable), the inclination angle of the orbit i \sim 70 \arcdeg, and the tilting angle of the disk i_{\rm prec} \sim 35 \arcdeg. These parameters are consistent with the recently derived binary parameters of T CrB.Comment: 6 pages including 2 figures, to be published in ApJ Letter

Asteroseismological Observations of the Central Star of the Planetary Nebula NGC 1501

We report on a global CCD time-series photometric campaign to decode the pulsations of the nucleus of the planetary nebula NGC1501. The star is hot and hydrogen-deficient, similar to the pre-white-dwarf PG 1159 stars. NGC1501 shows pulsational brightness variations of a few percent with periods ranging from 19 to 87 minutes. The variations are very complex, suggesting a pulsation spectrum that requires a long unbroken time series to resolve. Our CCD photometry of the star covers a two-week period in 1991 November, and used a global network of observatories. We obtained nearly continuous coverage over an interval of one week in the middle of the run. We have identified 10 pulsation periods, ranging from 5235 s down to 1154 s. We find strong evidence that the modes are indeed nonradial g-modes. The ratios of the frequencies of the largest-amplitude modes agree with those expected for modes that are trapped by a density discontinuity in the outer layers. We offer a model for the pulsation spectrum that includes a common period spacing of 22.3 s and a rotation period of 1.17 days; the period spacing allows us to assign a seismological mass of 0.55+/-0.03 Msun.Comment: 12 pages, AASTEX, 7 tables, 6 EPS figures, to appear in AJ, 12/96 Corrected version repairs table formatting and adds missing Table

U Sco 2010 outburst: a new understanding of the binary accretion disk and the secondary star

We present optical and NIR spectroscopic observations of U Sco 2010 outburst. From the analysis of lines profiles we identify a broad and a narrow component and show that the latter originates from the reforming accretion disk. We show that the accretion resumes shortly after the outburst, on day +8, roughly when the super-soft (SSS) X-ray phase starts. Consequently U Sco SSS phase is fueled (in part or fully) by accretion and should not be used to estimate $m_{\mathrm{rem}}$, the mass of accreted material which has not been ejected during the outburst. In addition, most of the He emission lines, and the HeII lies in particular, form in the accretion flow/disk within the binary and are optically thick, thus preventing an accurate abundance determination. A late spectrum taken in quiescence and during eclipse shows CaII H&K, the G-band and MgI b absorption from the secondary star. However, no other significant secondary star features have been observed at longer wavelengths and in the NIR band.Comment: Accepted for publication on A&A. 12 pages and 12 figures (a few are multiple figures

Transcriptional down-regulation of ccr5 in a subset of HIV+ controllers and their family members.

HIV +Elite and Viremic controllers (EC/VCs) are able to control virus infection, perhaps because of host genetic determinants. We identified 16% (21 of 131) EC/VCs with CD4 +T cells with resistance specific to R5-tropic HIV, reversed after introduction of ccr5. R5 resistance was not observed in macrophages and depended upon the method of T cell activation. CD4 +T cells of these EC/VCs had lower ccr2 and ccr5 RNA levels, reduced CCR2 and CCR5 cell-surface expression, and decreased levels of secreted chemokines. T cells had no changes in chemokine receptor mRNA half-life but instead had lower levels of active transcription of ccr2 and ccr5, despite having more accessible chromatin by ATAC-seq. Other nearby genes were also down-regulated, over a region of ~500 kb on chromosome 3p21. This same R5 resistance phenotype was observed in family members of an index VC, also associated with ccr2/ccr5 down-regulation, suggesting that the phenotype is heritable

Identification of the Mass Donor Star's Spectrum in SS 433

We present spectroscopy of the microquasar SS 433 obtained near primary eclipse and disk precessional phase Psi = 0.0, when the accretion disk is expected to be most ``face-on''. The likelihood of observing the spectrum of the mass donor is maximized at this combination of orbital and precessional phases since the donor is in the foreground and above the extended disk believed to be present in the system. The spectra were obtained over four different runs centered on these special phases. The blue spectra show clear evidence of absorption features consistent with a classification of A3-7 I. The behavior of the observed lines indicates an origin in the mass donor. The observed radial velocity variations are in anti-phase to the disk, the absorption lines strengthen at mid-eclipse when the donor star is expected to contribute its maximum percentage of the total flux, and the line widths are consistent with lines created in an A supergiant photosphere. We discuss and cast doubt on the possibility that these lines represent a shell spectrum rather than the mass donor itself. We re-evaluate the mass ratio of the system and derive masses of 10.9 +/- 3.1 Msun and 2.9 +/- 0.7 Msun for the mass donor and compact object plus disk, respectively. We suggest that the compact object is a low mass black hole. In addition, we review the behavior of the observed emission lines from both the disk/wind and high velocity jets.Comment: submitted to ApJ, 24 pages, 7 figure

Variability and multi-periodic oscillations in the X-ray light curve of the classical nova V4743 Sgr

The classical nova V4743 Sgr was observed with XMM-Newton for about 10 hours on April 4 2003, 6.5 months after optical maximum. At this time, this nova had become the brightest supersoft X-ray source ever observed. We present the results of a time series analysis performed on the X-ray light curve obtained in this observation, and in a previous shorter observation done with Chandra 16 days earlier. Intense variability, with amplitude as large as 40% of the total flux, was observed both times. Similarities can be found between the two observations in the structure of the variations. Most of the variability is well represented as a combination of oscillations at a set of discrete frequencies lower than 1.7 mHz. At least five frequencies are constant over the 16 day time interval between the two observations. We suggest that a periods in the power spectrum of both light curves at the frequency of 0.75 mHz and its first harmonic are related to the spin period of the white dwarf in the system, and that other observed frequencies are signatures of nonradial white dwarf pulsations. A possible signal with a 24000 sec period is also found in the XMM-Newton light curve: a cycle and a half are clearly identified. This period is consistent with the 24278 s periodicity discovered in the optical light curve of the source and thought to be the orbital period of the nova binary system.Comment: In press in Monthly Notices of the Royal Astronomical Societ

Deep infrared observations of the puzzling central X-ray source in RCW103

1E 161348-5055 (1E 1613) is a point-like, soft X-ray source originally identified as a radio-quiet, isolated neutron star, shining at the center of the 2000 yr old supernova remnant RCW103. 1E 1613 features a puzzling 6.67 hour periodicity as well as a dramatic variability over a time scale of few years. Such a temporal behavior, coupled to the young age and to the lack of an obvious optical counterpart, makes 1E 1613 a unique source among all compact objects associated to SNRs. It could either be the first low-mass X-ray binary system discovered inside a SNR, or a peculiar isolated magnetar with an extremely slow spin period. Analysis of archival IR observations, performed in 2001 with the VLT/ISAAC instrument, and in 2002 with the NICMOS camera onboard HST unveils a very crowded field. A few sources are positionally consistent with the refined X-ray error region that we derived from the analysis of 13 Chandra observations. To shed light on the nature of 1E 1613, we have performed deep IR observations of the field with the NACO instrument at the ESO/VLT, searching for variability. We find no compelling reasons to associate any of the candidates to 1E 1613. On one side, within the frame of the binary system model for the X-ray source, it is very unlikely that one of the candidates be a low-mass companion star to 1E 1613. On the other side, if the X-ray source is an isolated magnetar surrounded by a fallback disc, we cannot exclude that the IR counterpart be hidden among the candidates. If none of the potential counterparts is linked to the X-ray source, 1E 1613 would remain undetected in the IR down to Ks>22.1. Such an upper limit is consistent only with an extremely low-mass star (an M6-M8 dwarf) at the position of 1E 1613, and makes rather problematic the interpretation of 1E 1613 as an accreting binary system.Comment: 26 pages, 5 figures. Accepted for publication in Ap