Y. Lipkin

Tel Aviv University, Tell Afif, Tel Aviv, Israel

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Publications (60)215.7 Total impact

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    ABSTRACT: KPD 1930+2752 is a short-period pulsating subdwarf B (sdB) star. It is also an ellipsoidal variable with a known binary period just over two hours. The companion is most likely a white dwarf and the total mass of the system is close to the Chandresakhar limit. In this paper we report the results of Whole Earth Telescope (WET) photometric observations during 2003 and a smaller multisite campaign from 2002. From 355 hours of WET data, we detect 68 pulsation frequencies and suggest an additional 13 frequencies within a crowded and complex temporal spectrum between 3065 and 6343 $\mu$Hz (periods between 326 and 157 s). We examine pulsation properties including phase and amplitude stability in an attempt to understand the nature of the pulsation mechanism. We examine a stochastic mechanism by comparing amplitude variations with simulated stochastic data. We also use the binary nature of KPD 1930+2752 for identifying pulsation modes via multiplet structure and a tidally-induced pulsation geometry. Our results indicate a complicated pulsation structure that includes short-period ($\approx 16$ h) amplitude variability, rotationally split modes, tidally-induced modes, and some pulsations which are geometrically limited on the sdB star. Comment: 30 pages, 17 figures, 11 tables. Accepted for publication by MNRAS
    11/2010;
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    ABSTRACT: Aims: We present a detailed analysis of OGLE 2004-BLG-482, a relatively high-magnification single-lens microlensing event which exhibits clear extended-source effects. These events are relatively rare, but they potentially contain unique information on the stellar atmosphere properties of their source star, as shown in this study. Methods: Our dense photometric coverage of the overall light curve and a proper microlensing modelling allow us to derive measurements of the OGLE 2004-BLG-482 source star's linear limb-darkening coefficients in three bands, including standard Johnson-Cousins I and R, as well as in a broad clear filter. In particular, we discuss in detail the problems of multi-band and multi-site modelling on the expected precision of our results. We also obtained high-resolution UVES spectra as part of a ToO programme at ESO VLT from which we derive the source star's precise fundamental parameters. Results: From the high-resolution UVES spectra, we find that OGLE 2004-BLG-482's source star is a red giant of MK type a bit later than M3, with Teff = 3667 +/- 150 K, log g = 2.1 +/- 1.0 and an assumed solar metallicity. This is confirmed by an OGLE calibrated colour-magnitude diagram. We then obtain from a detailed microlensing modelling of the light curve linear limb-darkening coefficients that we compare to model-atmosphere predictions available in the literature, and find a very good agreement for the I and R bands. In addition, we perform a similar analysis using an alternative description of limb darkening based on a principal component analysis of ATLAS limb-darkening profiles, and also find a very good agreement between measurements and model predictions.
    Astronomy and Astrophysics 12/2009; 525:15. · 5.08 Impact Factor
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    ABSTRACT: The Type II-P supernova SN 2004dj in the nearby galaxy NGC 2403 occurred at a position coincident with object 96 in the list of luminous stars and clusters in this galaxy published by Sandage in 1984. The coincidence is established definitively through astrometric registration of our ground-based archival images of NGC 2403 with our recent images showing the SN. The archival images show that Sandage 96 is slightly resolved from the ground. Preoutburst blue spectrograms obtained by Humphreys & Aaronson reveal that Sandage 96 has a composite spectrum, dominated in the blue region by A- and B-type stars, while infrared photometry shows that Sandage 96 also contains red supergiants. These results demonstrate that Sandage 96 is a young compact cluster. We have studied the stellar population of Sandage 96, using published photometric measurements combined with a χ2 fitting code. We derive a cluster age of 13.6 Myr, a reddening of E(4405 - 5495) = 0.172, and a total stellar mass of 24,000 M☉. For this cluster age, the SN progenitor had a main-sequence mass of 15 M☉. Postoutburst photometry of Sandage 96 may establish whether the progenitor was a red or blue supergiant.
    The Astrophysical Journal 12/2008; 615(2):L113. · 6.73 Impact Factor
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    ABSTRACT: We present densely sampled BVRI light curves of the optical transient associated with the gamma-ray burst (GRB) 030329, the result of a coordinated observing campaign conducted at five observatories. Augmented with published observations of this GRB, the compiled optical data set contains 2687 photometric measurements, obtained between 78 minutes and 79 days after the burst. This data set allows us to follow the photometric evolution of the transient with unprecedented detail. We use the data to constrain the light curve of the underlying supernova (SN) 2003dh and show that it evolved faster than and was probably somewhat fainter than the Type Ic SN 1998bw, associated with GRB 980425. We find that our data can be described by a broken power-law decay perturbed by a complex variable component. The early- and late-time decay slopes are determined to be α1 ≈ 1.1 and α2 ≈ 2. Assuming this single-break power-law model, we constrain the break to lie between ~3 and ~8 days after the burst. This simple, singly broken power-law model, derived only from the analysis of our optical observations, may also account for available multiband data, provided that the break happened ~8 days after the burst. The more complex double-jet model of Berger et al. provides a comparable fit to the optical, X-ray, millimeter, and radio observations of this event. The unique early coverage available for this event allows us to trace the color evolution of the afterglow during the first hours after the burst. We detect a significant change in optical colors during the first day. Our color analysis is consistent with a cooling-break frequency sweeping through the optical band during the first day. The light curves of GRB 030329 reveal a rich array of variations, superposed over the mean power-law decay. We find that the early variations (8 days after the burst) are asymmetric, with a steep rise followed by a relatively slower (by a factor of about 2) decline. The variations maintain a similar timescale during the first 4 days and then get significantly longer. The structure of these variations is similar to those previously detected in the afterglows of several GRBs.
    The Astrophysical Journal 12/2008; 606(1):381. · 6.73 Impact Factor
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    ABSTRACT: We develop a new method of modeling microlensing events based on a Monte Carlo simulation that incorporates both a Galactic model and the constraints imposed by the observed characteristics of the event. The method provides an unbiased way to analyze the event, especially when parameters are poorly constrained by the observed light curve. We apply this method to search for planetary companions of the lens in OGLE-2003-BLG-423, whose maximum magnification Amax = 256 ± 43 (or Amax = 400 ± 115 from the light-curve data alone) is the highest among single-lens events ever recorded. The method permits us for the first time to place constraints directly in the planet mass-projected physical separation plane rather than in the mass ratio-Einstein radius plane as was done previously. For example, Jovian-mass companions of main-sequence stars at 2.5 AU are excluded with 80% efficiency.
    The Astrophysical Journal 12/2008; 616(2):1204. · 6.73 Impact Factor
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    Y. M. Lipkin, E. M. Leibowitz
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    ABSTRACT: Photometric observations of V4633 Sgr (Nova Sagittarii 1998) during 1998-2005 reveal the presence of a stable photometric periodicity at P1=180.8 min which is probably the orbital period of the underlying binary system. A second period was present in the light curve of the object for six years. Shortly after the nova eruption it was measured as P2=185.6 min. It has decreased monotonically in the following few years reaching the value P2=183.9 min in 2003. In 2004 it was no longer detectable. We suggest that the second periodicity is the spin of the magnetic white dwarf of this system that rotates nearly synchronously with the orbital revolution. According to our interpretation, the post-eruption evolution of Nova V4633 Sgr follows a track similar to the one taken by V1500 Cyg (Nova Cygni 1975) after that nova eruption, on a somewhat longer time scale. The asynchronism is probably the result of the nova outburst that lead to a considerable expansion of the white dwarf's photosphere. The increase in the moment of inertia of the star was associated with a corresponding decrease in its spin rate. Our observations have followed the spinning up of the white dwarf resulting from the contraction of its outer envelope as the star is slowly retuning to its pre-outburst state. It is thus the second known asynchronous polar classical nova. Comment: 6 pages, 8 figures. Accepted for publication in MNRAS
    Monthly Notices of the Royal Astronomical Society 05/2008; · 5.52 Impact Factor
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    ABSTRACT: We present new spectroscopic and photometric data of the type Ibn supernovae 2006jc, 2000er and 2002ao. We discuss the general properties of this recently proposed supernova family, which also includes SN 1999cq. The early-time monitoring of SN 2000er traces the evolution of this class of objects during the first few days after the shock breakout. An overall similarity in the photometric and spectroscopic evolution is found among the members of this group, which would be unexpected if the energy in these core-collapse events was dominated by the interaction between supernova ejecta and circumstellar medium. Type Ibn supernovae appear to be rather normal type Ib/c supernova explosions which occur within a He-rich circumstellar environment. SNe Ibn are therefore likely produced by the explosion of Wolf-Rayet progenitors still embedded in the He-rich material lost by the star in recent mass-loss episodes, which resemble known luminous blue variable eruptions. The evolved Wolf-Rayet star could either result from the evolution of a very massive star or be the more evolved member of a massive binary system. We also suggest that there are a number of arguments in favour of a type Ibn classification for the historical SN 1885A (S-Andromedae), previously considered as an anomalous type Ia event with some resemblance to SN 1991bg. Comment: 17 pages including 12 figures and 4 tables. Slightly revised version, conclusions unchanged, 1 figure added. Accepted for publication in MNRAS
    Monthly Notices of the Royal Astronomical Society 01/2008; · 5.52 Impact Factor
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    ABSTRACT: The results of a world-wide coordinated observational campaign on the broad-lined Type Ic SN 2003jd are presented. In total, 74 photometric data points and 26 spectra were collected using 11 different telescopes. SN 2003jd is one of the most luminous SN Ic ever observed. A comparison with other Type Ic supernovae (SNe Ic) confirms that SN 2003jd represents an intermediate case between broad-line events (2002ap, 2006aj), and highly energetic SNe (1997ef, 1998bw, 2003dh, 2003lw), with an ejected mass of M_{ej} = 3.0 +/- 1 Mo and a kinetic energy of E_{k}(tot) = 7_{-2}^{+3} 10^{51} erg. SN 2003jd is similar to SN 1998bw in terms of overall luminosity, but it is closer to SNe 2006aj and 2002ap in terms of light-curve shape and spectral evolution. The comparison with other SNe Ic, suggests that the V-band light curves of SNe Ic can be partially homogenized by introducing a time stretch factor. Finally, due to the similarity of SN 2003jd to the SN 2006aj/XRF 060218 event, we discuss the possible connection of SN 2003jd with a GRB. Comment: 19 pages, 19 figures, Accepted for publication in MNRAS
    10/2007;
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    ABSTRACT: While Abell 43 is entering the PG 1159 instability strip, in fact as an "hybrid-PG 1159" nucleus of a planetary nebula, PG 0122+200 presently defines its red edge. So these two stars define the limits of the instability strip along the evolutionary sequence from the planetary nebula nuclei to the pre-white dwarf PG 1159 stars. We describe the new observations that have been obtained recently on these two extreme PG 1159 pulsators. Abell 43, the second discovered "hybrid-PG 1159" pulsator after HS 2324+3944, is a multi-periodic low amplitude pulsator with the longest period observed so far in PG 1159 pulsators. As it shows amplitude variations, follow-up observations are needed to obtain a sufficient number of frequencies to start an asteroseismological analysis. We summarize the status of the presently available data. On PG 0122+200, new observations were obtained in 2001 and 2002. Together with previous data, they allow us to detect 23 frequencies, including seven triplets and two single frequencies. We interpret the triplets as ℓ=1 modes split by rotation and confirm an average rotation period of 1.55 days. From the up-dated average period spacing of 22.9 s, we derive a mass of 0.59 ± 0.02 Msun, in better agreement with the spectroscopically derived mass than from previous estimates, and a luminosity log(L/Lsun)= 1.3 ± 0.5. The uncertainty on the luminosity is dominated by the poorly determined surface gravity. We discuss the impact of that new mass determination on the predicted neutrino luminosity.
    08/2007; 372:641.
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    ABSTRACT: Context.The variable pre-white dwarf PG 1159 stars (GW Vir) are $g$-mode non-radial pulsators. Asteroseismology puts strong constraints on their global parameters and internal structure. PG 0122+200 defines the red edge of the instability strip and its evolutionary timescale is predicted to be dominated by neutrino emission. Its study offers the opportunity to better understand the instability mechanism and to validate the physics of the neutrino production in dense plasma.Aims.To achieve such a goal requires determining precisely its fundamental parameters. This is the goal of this paper.Methods.We present new multi-site photometric observations obtained in 2001 and 2002. Together with previous data, they allow us to detect 23 frequencies, composed of 7 triplets and 2 single frequencies, which are used to constrain its internal structure and derive its fundamental parameters.Results.All the observed frequencies correspond to $\ell$=1 $g$-modes. The period distribution shows a signature of mode trapping from which we constrain the He-rich envelope mass fraction to be -6.0$\leq \log(q_{y}) \leq$ -5.3. The comparison of the mode trapping amplitudes among GW Vir stars suggests that the mass-loss efficiency must decrease significantly below $T_{\rm eff}\leq$ 140 kK. We measure an average period spacing of 22.9 s from which we derive a mass of 0.59$\pm$0.02 $M_{\odot}$. From the triplets we measure a mean rotational splitting of 3.74 $\mu$Hz and a rotational period of 1.55 days. We derive an upper limit to the magnetic field of $B\leq4\times10^{3}$ G. The luminosity ($\log L/L_{\odot}$ = 1.3$\pm$0.5) and the distance ($D = 0.7^{\rm +1.0}_{\rm -0.4}$ kpc) are only weakly constrained due to the large uncertainty on the spectroscopically derived surface gravity and the absence of a measured parallax.Conclusions.From the asteroseismic mass, the ratio of the neutrino luminosity on the photon luminosity is 1.6$\pm$0.2 confirming that the PG 0122+200 evolutionary time scale should be dominated by neutrino cooling. A measurement of $\dot{P}$ for the largest amplitude untrapped modes should verify this prediction.
    Astronomy and Astrophysics 01/2007; · 5.08 Impact Factor
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    ABSTRACT: Understanding and quantifying the contribution of known classes of transient and variable sources is an important lesson to be learned from the manifold of pre-cursors programs of the near-future large synoptic sky survey programs like SkyMapper, Pan-STARRS and LSST. With this goal in mind, we undertook photometric and spectroscopic follow-up observations of three recently reported unidentified transients. For two sources, WFI J132813.7-214237 and WFI J161953.3+031909, we show that unfortunate coincidences lead to their previous designation as transients. While the former is now interpreted as the spatial coincidence of a solar system object with faint background star, the latter is merely a cataclysmic variable unfortunately caught in and out of eclipse. The third candidate, ROTSE3 J160213.1-021311.7 is identified as an SU UMa-type dwarf novae with quiescent brightness of R~22.7 and an outburst amplitude of about 5 mag. The fourth event, SDSS-SN15207, similarly shows evidence for a dwarf nova origin. Our main conclusion is that cataclysmic variables in their various avata rs will contribute moderately to the population of transient objects.
    The Astrophysical Journal 11/2006; 664(1). · 6.73 Impact Factor
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    ABSTRACT: In this article we present the results of 215 h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (T_eff = 35 000 K, log g = 5.8, log N(He)/N(H) = -1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55 μHz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies are found: three of them at 7704.92, 9380.17 and 14511.10 μHz were already present in the discovery run with small differences in frequency, probably due to 1-day aliasing effects. The peak at 7704.92 μHz belongs to a triplet of almost equally spaced frequencies that could be due to rotational splitting and would imply a rotational period of about 1.6 days. Based on the results of this article, a detailed asteroseismic analysis of PG 1325+101 is presented in a separate paper (Charpinet et al. 2006b, A&A, 459, 565, Paper II).
    Astronomy and Astrophysics 11/2006; 459(2):557-564. · 5.08 Impact Factor
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    ABSTRACT: We present a detailed analysis of the rapidly pulsating subdwarf B star (or EC14026 star) PG 1325+101. This analysis exploits the outcome of dedicated multisite observations using time-series photometry that revealed the presence of (at least) 15 periodicities in the luminosity modulation of this star (Silvotti et al. 2006, A&A, 459, 557, Paper I). Based on high-S/N, medium-resolution spectra obtained at the Steward Observatory's 2.3 m Telescope and at the 6.5 m MMT Telescope, new NLTE spectroscopic derivations of the atmospheric parameters of PG 1325+101 are presented. The mean values of T_eff = 35 050 ± 220 K, log g=5.81 ± 0.04, and log N(He)/N(H) = -1.70± 0.02 are in agreement with previous determinations, but are significantly more accurate. These improved spectroscopic parameters are essential for isolating a unique asteroseismic model solution for the observed pulsation spectrum of PG 1325+101. Using the "forward modeling" approach, our combined spectroscopic and asteroseismic analysis leads objectively to the identification of the (k, ℓ) indices of the 12 independent modes observed in this star, and to the determination of its structural parameters. The periods correspond to low-order acoustic modes with adjacent values of k and having degrees ℓ=0-4. They define a band of unstable modes, in agreement with nonadiabatic pulsation theory. The average dispersion achieved between the observed periods and the periods of the corresponding theoretical modes of the optimal model is only 0.46% (˜ 0.54 s), comparable to the results from similar analyses of other EC14026 stars analysed to date. The inferred structural parameters of PG 1325+101 are Teff= 35 050 ± 220 K, log g=5.811±0.004, log M{env}/M*=-4.18±0.10, M*=0.50±0.01 M⊙ (i.e., close to the canonical mass of extreme horizontal branch stars), R/R⊙=0.145±0.002, and L/L⊙=28.3±1.5. In addition, by combining detailed model atmosphere calculations with V=14.019±0.012, we estimate that this star has an absolute visual magnitude M_V=4.45±0.04 and is located at a distance of d=820±21 pc. Finally, the presence of fine structure in the observed period spectrum suggests a rotation period of P=1.6±0.2 days, leading to an equatorial velocity of Veq=4.6±0.6 km s-1. Hence, asteroseismic evidence suggests that PG 1325+101 is a slow rotator, a conclusion reinforced by the limit V sin i < 20-30 km s-1, which we determined by modeling the He I 4471 line in our 1 Å-resolution MMT spectrum.
    Astronomy and Astrophysics 11/2006; 459(2):565-576. · 5.08 Impact Factor
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    ABSTRACT: We present the results of 215h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (Teff=35000K, logg=5.8, logN(He)/N(H)=-1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55{mu}Hz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies are found: three of them at 7704.92, 9380.17 and 14511.10{mu}Hz were already present in the discovery run with small differences in frequency, probably due to 1-day aliasing effects. The peak at 7704.92{mu}Hz belongs to a triplet of almost equally spaced frequencies that could be due to rotational splitting and would imply a rotational period of about 1.6 days. Based on the results of this article, a detailed asteroseismic analysis of PG 1325+101 is presented in a separate paper (Charpinet et al., 2996A&A...459..565C, Paper II). (1 data file).
    VizieR Online Data Catalog. 09/2006;
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    ABSTRACT: The classical nova V4743 Sgr was observed with XMM–Newton for about 10 h on 2003 April 4, 6.5 months after optical maximum. At this time, this nova had become the brightest supersoft X-ray source ever observed. In this paper, we present the results of a time-series analysis performed on the X-ray light curve (LC) obtained in this observation, and in a previous shorter observation done with Chandra 16 d earlier. Intense variability, with amplitude as large as 40 per cent 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 d time interval between the two observations. We suggest that a period in the power spectrum of both LCs at the frequency of 0.75 mHz and its first harmonic are related to the spin period of the white dwarf (WD) in the system, and that other observed frequencies are signatures of non-radial WD pulsations. A possible signal with a 24 000 s period is also found in the XMM–Newton LC: a cycle and a half are clearly identified. This period is consistent with the 24 278 s periodicity discovered in the optical LC of the source and thought to be the orbital period of the nova binary stellar system.
    Monthly Notices of the Royal Astronomical Society 08/2006; 371(1):424 - 430. · 5.52 Impact Factor
  • Minor Planet Circulars. 02/2005;
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    ABSTRACT: This figure replaces Figure 2 in the original Letter. The figure was generated automatically several times by a computer code, and during the revision process, an incorrect version was submitted. In the published version, only a single solution (the young one) was apparent in the likelihood contour plot, but the existence of a second, older one was discussed in the text. The second peak had disappeared because of an incorrect choice of contour levels. The same data are plotted here with a lower minimum contour, thus revealing the existence of the older solution.
    The Astrophysical Journal 01/2005; 618(1). · 6.73 Impact Factor
  • E. O. Ofek, Y. M. Lipkin, J. Dann
    GRB Coordinates Network. 01/2005;
  • E. O. Ofek, Y. Lipkin
    GRB Coordinates Network. 01/2005;
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    ABSTRACT: We present the light curve and time series analysis of classical novae and dwarf novae systems monitored/observed with the 1.5 m Russian-Turkish Joint telescope (RTT150) at the TÜBITAK (The Scientific and Technical Research Council of Turkey) National Observatory in Antalya, Turkey. As part of a large program on CCD photometry of Cataclysmic Variables, V2275 Cyg (N 2001 No.2), RW UMi, FO Per and PX And were observed for a total of about 25 nights. The results on V2275 Cyg show that the system has a period of 0.463±0.014 or the 1-d alias 0.316±0.007 with a wide eclipse-like pattern (IAUC 8074). The power spectral analysis of the data on RW UMi reveal possible periodicities at around several frequencies (eg., 14.4, 16.7, 19, 30, 39, 46, 68, 108 in cycles per day) that could be interpreted as the binary period, spin period of the white dwarf and/or orbital sidebands of the system. We find that the radial velocity profiles of H-alpha lines and the photometry of the Dwarf Nova FO Per indicates the possible presence of a period around 0.1828 d.
    12/2004: pages 233-242;