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R. E. Mennickent

Publications and source records attributed to R. E. Mennickent.

At least 73 records · Page 4Linked to original sources
arXiv2010

A study of the interacting binary V 393 Scorpii

We present high resolution J-band spectroscopy of V 393 Sco obtained with the CRIRES at the ESO Paranal Observatory along with a discussion of archival IUE spectra and published broad band magnitudes. The best fit to the spectral energy distribution outside eclipse gives $T_{1}$= 19000 $\pm$ 500 $K$ for the gainer, $T_{2}$= 7250 $\pm$ 300 $K$ for the donor, $E(B-V)$= 0.13 $\pm$ 0.02 mag. and a distance of $d$= 523 $\pm$ 60 pc, although circumstellar material was not considered in the fit. We argue that V 393 Sco is not a member of the open cluster M7. The shape of the He I 1083 nm line shows orbital modulations that can be interpreted in terms of an optically thick pseudo-photosphere mimicking a hot B-type star and relatively large equatorial mass loss through the Lagrangian L3 point during long cycle minimum. IUE spectra show several (usually asymmetric) absorption lines from highly ionized metals and a narrow L$α$ emission core on a broad absorption profile. The overall behavior of these lines suggests the existence of a wind at intermediate latitudes. From the analysis of the radial velocities we find $M_{2}/M_{1}$= 0.24 $\pm$ 0.02 and a mass function of $f$= 4.76 $\pm$ 0.24 M$\odot$. Our observations favor equatorial mass loss rather than high latitude outflows as the cause for the long variability.

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arXiv2009

Light Curves of Galactic Eclipsing Double Periodic Variables

We present results of the investigation of the nature of double periodic variables (DPVs). We have selected a sample of Galactic eclipsing DPVs for a multiwavelength photometric study aimed to reveal their nature. The short orbital periodicity and the cyclic variability are decoupled and separately investigated. Shapes of orbital light curves are consistent with semi-detached binaries. The amplitude of the long cycle is always larger in redder bandpasses.

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arXiv2009

The class of interacting binaries Double Periodic Variables

We introduce the class of intermediate mass binaries named Double Periodic Variables (DPVs), characterized by orbital photometric variability (ellipsoidal or eclipsing) in time scales of few days and a long photometric cycle lasting roughly 33 times the orbital period. After a search conducted in the OGLE and ASAS catalogues, we identified 114 of these systems in the Magellanic Clouds and 11 in the Galaxy. We present results of our photometric and spectroscopic campaigns on DPVs conducted during the last years, outlining their main observational characteristics. We present convincing evidence supporting the view that DPVs are semidetached interacting binaries with optically thick discs around the gainer, that experience regular cycles of mass loss into the interstellar medium. The mechanism regulating this long-term process still is unknown but probably is related to relaxation cycles of the circumprimary disc. A key observational fact is the modulation of the FWHM of HeI 5875 with the long cycle in V393 Sco. The DPV evolution stage is investigated along with their relationship to Algols and W Serpentid stars. We conclude that DPVs can be used to test models of non-conservative binary evolution including the formation of circumbinary discs.

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arXiv2009

Observations of three pre-cataclysmic variables from the Edinburgh-Cape Blue Object Survey

We present light curves and time-resolved spectroscopy of the three candidate pre-cataclysmic binaries EC 12477-1738, EC 13349-3237, and EC 14329-1625. We determine the orbital period for EC 12477-1738 as 0.362 d, thus confirming the value previously reported. A similar period, P=0.350 d, is found for EC 14329-1625. Both systems incorporate a medium-hot white dwarf (T = 15000-20000 K) and an M3V secondary star. The third pre-CV, EC 13349-3237, is the youngest of the three, with a hot WD (T ~ 35000 K), and it also has the longest period P=0.469 d. It furthermore turns out to be one of the still rare pre-CVs with a comparatively early-type, M1V, secondary star, which will eventually evolve into a CV above the period gap.

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arXiv2009

Interacting Binary Star Environments and the W Ser - DPV - Algol Connection

Recent work on some kinds of interacting binaries is summarized, with emphasis on Cataclysmic Variables, Algol-like variables and the recently discovered Double Periodic Variables (DPVs). The sequence W Serpentids (very massive with irregular variability and large mass loss) $\to$ DPVs (less massive with regular variability and ciclic mass loss) $\to$ Algols (even less massive with small mass loss) could correspond to an evolutionary sequence, and illustrate the importance of the mass transfer rate in shaping observable and mass loss properties for these systems.

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arXiv2009

Unveiling the phenomenon of Double Periodic Variables

In this paper we give a brief report of our recent research on Double Periodic Variables (DPVs), including the discovery of DPVs in the Galaxy and some insights on the nature of their long-cycle variability.

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arXiv2009

L-band spectra of 13 outbursting Be stars

We present new L-band spectra of 13 outbursting Be stars obtained with ISAAC at the ESO Paranal observatory. These stars can be classified in three groups depending on the presence/absence of emission lines and the strength of Br$α$ and Pf$γ$ emission lines relative to those of Humphreys lines from transitions 6--14 to the end of the series. These groups are representative of circumstellar envelopes with different optical depths. For the group showing Br$α$ and Pf$γ$ lines stronger than Humphreys lines, the Humphreys decrement roughly follow the Menzel case-B for optically thin conditions. For the group showing comparable Br$α$, Pf$γ$ and Humphreys emission line strengths, the Humphreys decrements moves from an optically thin to an optically thick regime at a transition wavelength which is characteristic for each star, but typically is located around 3.65--3.75 $μ$m (transitions 6--19 and 6--17). Higher order Humphreys lines probe optically thin inner regions even in the optically thicker envelopes. We find evidence of larger broadening in the infrared emission lines compared with optical lines, probably reflecting larger vertical velocity fields near the star. The existence of the aforementioned groups is in principle consistent with the proposed description by de Wit et al. (2006) for Be star outbursts in terms of the ejection of an optically thick disk that expands and becomes optically thin before dissipation into the interstellar medium. Time resolved L-band spectroscopy sampling the outburst cycle promises to be an unique tool for testing Be star disk evolution.

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arXiv2008

A likely optical counterpart of the G292.0+1.8 pulsar wind nebula

G292.0+1.8 is the Cas A-like supernova remnant containing the young pulsar PSR J1124-5916, which powers a compact torus-like pulsar wind nebula with a jet visible in X-rays. We have performed deep optical observations of the pulsar field to detect the optical counterpart of the pulsar and its nebula. The observations were carried out using the direct imaging mode of FORS2 at the ESO VLT/UT1 telescope in the V, R, and I bands. We also analyzed archival images obtained with the Chandra/ACIS-I, ACIS-S, and HRC-S in X-rays. In all three optical bands we detect a faint elliptical nebulosity, whose brightness peak and center position are consistent at a sub-arcsecond level with the X-ray position of the pulsar. The field is densely packed with background stars, but after subtraction of these stars the morphology of the object and the orientation of its major axis appear to be in a good agreement with the brightest inner part of the pulsar nebula torus region seen almost edge on in X-rays. Within the nebulosity we do not resolve any point-like optical object that could be identified with the pulsar and estimate its contribution to the observed nebulosity flux as <~20%. Extracting the X-ray spectrum from the physical region equivalent to the optical source position and extent and combining that with the measured optical fluxes, we compile a tentative multi-wavelength spectrum of the inner part of the nebula. Within uncertainties of the interstellar extinction towards G292.0+1.8 it is reminiscent of either the Crab or PSR B540-69 and J0205+6449 pulsar wind nebula spectra. The position, morphology, and spectral properties of the detected nebulosity suggest that it is the likely optical counterpart of the pulsar plus its wind nebula system in G292.0+1.8.

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arXiv2008

The eclipsing LMC star OGLE05155332--6925581: a clue for Double Periodic Variables

We investigate the nature of OGLE05155332-6925581, one of the brightest members of the enigmatic group of Double Periodic Variables (DPVs) recently found in the Magellanic Clouds. The modeling of archival orbital light curves (LCs), along with the analysis of the radial velocities suggest that this object is a semi--detached binary with the less massive star transferring matter to the more massive and less evolved star, in an Algol--like configuration. We find evidence for additional orbital variability and H$α$ emission, likely caused by an accretion disc around the primary star. As in the case of $βLyr$ the circumprimary disc seems to be more luminous than the primary, but we do not detect orbital period changes. We find that the LC follows a loop in the color--magnitude diagram during the long cycle; the system is redder when brighter and the rising phase is bluer than during decline. Infrared excess is also present. The source of the long--term periodicity is not eclipsed, indicating its circumbinary origin. Strong asymmetries, discrete absorption components (DACs) and a $γ$ shift are new and essential observational properties in the infrared H I lines. The DACs strength and RV follow a saw--teeth pattern during the orbital cycle. We suggest that the system experiences supercycles of mass outflow feeding a circumbinary disc. Mass exchange and mass loss could produce comparable but opposite effects in the orbital period on a long time scale, resulting in a quasi--constancy of this parameter.

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arXiv2008

Unveiling the nature of six HMXBs through IR spectroscopy

The International Gamma-Ray Astrophyiscs Laboratory (INTEGRAL) is discovering a large number of new hard X-ray sources, many of them being HMXBs. The identification and spectral characterization of their optical/infrared counterparts is a necessary step to undertake detailed study of these systems. In particular, the determination of the spectral type is crucial in the case of the new class of Supergiant Fast X-ray Transients (SFXTs), which show X-ray properties common to other objects. We used the ESO/NTT SofI spectrograph to observe proposed IR counterparts to HMXBs, obtaining Ks medium resolution spectra (R = 1320) with a S/N >= 100. We classified them through comparison with published atlases. We were able to spectrally classify the six sources. This allowed us to ascribe one of them to the new class of SFXTs and confirm the membership of two sources to this class. We confirmed the spectral classification, derived from optical spectroscopy, of a known system, 4U 1907-09, showing for the first time its infrared spectrum. The spectral classification was also used to estimate the distance of the sources. We compared the extinction as derived from X-ray data with effective interstellar extinction obtained from our data, discussing the absorption component due to the circumstellar environment, which we observed in four systems; in particular, intrinsic absorption seems to emerge as a typical feature of the entire class of SFXTs.

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arXiv2008

Two Be stars in the Small Magellanic Cloud with B[e]-like properties

We present an analysis of UVES and MIKE (ground based) high resolution and Far Ultraviolet Spectroscopic Explorer spectra of two novel and photometrically variable bright blue stars in the SMC; OGLE004336.91-732637.7 and the periodically occulted star OGLE004633.76-731204.3. The light curves of these stars exhibit multiple frequencies, and their spectra are similar. The latter are dominated by absorption/emission features produced in a circumstellar (CS) envelope whereas photospheric features are barely visible and forbidden emission lines are not visible. Modeling of spectral features indicates similar physical conditions for the CS envelope in both stars. An optically thick, slowly and thermally stratified disk. OGLE004633.76-731204.3 is noteworthy in showing blue discrete absorption components ("BACs") in their spectra possibly indicating the shock interaction between high velocity and low velocity material. Optical spectra from two spectra separated by 5 years show little change in the radial velocity over this period. However because these observations happen to be made in roughly similar phases over their long period, these suggest only that the stars are not in close binaries. We interpret the occultations and additional photometric nearly periodic variability in OGLE004633.76-731204.3 as due to covering of the star by a density modulation in a sector of a quasi-Keplerian circumstellar disk. Altogether, we suggest that these stars are prototypes of a larger group of stars, which we dub the "bgBe's" and discuss their similarities and differences with respect to the well known sgB[e] variables. Although OGLE004336.91-732637.7 appears to be a member the open cluster NGC 242, the evolutionary context of these stars is unclear.

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arXiv2008

Variability in the cycle length of the supersoft source RX J0513.9-6951

The supersoft X-ray binary RX J0513.9-6951 shows cyclic changes between optical-low / X-ray-on states and optical-high / X-ray-off states. It is supposed to be accreting close to the Eddington-critical limit and driven by "accretion wind evolution". We seek to derive the variations in the characteristic time scales of the long-term optical light curve and to determine the implications for the physical parameters of the system. We used existing and new optical monitoring observations covering a total time span of 14 years and compared the durations of the low and high states with the model calculations of Hachisu & Kato. The cycle lengths and especially the durations of the optical high states show a longterm modulation with variations that, according to the accretion wind evolution model, would imply variations in the mass transfer rate by a factor of 5 on timescales of years.

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arXiv2007

Possible optical detection of a fast, nearby radio pulsar PSR B1133+16

Aims: We performed deep optical observations of the field of an old, fast-moving radio pulsar PSR B1133+16 in an attempt to detect its optical counterpart and a bow shock nebula. Methods: The observations were carried out using the direct imaging mode of FORS1 at the ESO VLT/UT1 telescope in the B, R, and H_alpha bands. We also used archival images of the same field obtained with the VLT in the B band and with the Chandra/ACIS in X-rays. Results: In the B band we detected a faint (B=28.1+/-0.3) source that may be the optical counterpart of PSR B1133+16, as it is positionally consistent with the radio pulsar and with the X-ray counterpart candidate published earlier. Its upper limit in the R band implies a color index B-R <0.5, which is compatible with the index values for most pulsars identified in the optical range. The derived optical luminosity and its ratio to the X-ray luminosity of the candidate are consistent with expected values derived from a sample of pulsars detected in both spectral domains. No Balmer bow shock was detected, implying a low density of ambient matter around the pulsar. However, in the X-ray and H_alpha images we found the signature of a trail extending ~4"-5" behind the pulsar and coinciding with the direction of its proper motion. If confirmed by deeper studies, this is the first time such a trail has been seen in the optical and X-ray wavelengths. Conclusions: Further observations at later epochs are necessary to confirm the identification of the pulsar by the candidate's proper motion measurements.

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arXiv2007

The remarkable properties of the symbiotic star AE Circinus

We present new optical spectroscopy and photometry, 2MASS infrared observations and 24 years of combined AAVSO and AFOEV photometry of the symbiotic star candidate æ. The long-term light curve is characterized by outbursts lasting several years and having a slow decline of $\sim 2 \times 10^{-4}$ mag/day. The whole range of variability of the star in the $V$ band is about 4 magnitudes. The periodogram of the photometric data reveals strong signals at $\sim$ 342 and 171 days. The presence of the emission feature at $λ$ 6830 Åat minimum and the detection of absorption lines of a $\sim$ K5 type star confirm the symbiotic classification and suggest that AE Cir is a new member of the small group of s-type yellow symbiotic stars. We estimate a distance of 9.4 kpc. Our spectrum taken at the high state shows a much flatter spectral energy distribution, the disappearance of the $λ$ 6830 Åemission feature and the weakness of the He II 4686 emission relative to the Balmer emission lines. Our observations indicate the presence of emission line flickering in time scales of minutes in 2001. The peculiar character of æis revealed in the visibility of the secondary star at the high and low state, the light curve resembling a dwarf nova superoutburst and the relatively short low states. The data are hard to reconciliate with standard models for symbiotic star outbursts.

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arXiv2007

A Catalogue of Be Stars in the Direction of the Galactic Bulge

Detailed studies of Be stars in environments with different metallicities like the Magellanic Clouds or the Galactic bulge are necessary to understand the formation and evolution mechanisms of the circumstellar disks. However, a detailed study of Be stars in the direction of the bulge of our own galaxy has not been performed until now. We report the first systematic search for Be star candidates in the direction of the Galactic Bulge. We present the catalogue, give a brief description of the stellar variability seen, and show some light curve examples. We searched for stars matching specific criteria of magnitude, color and variability in the I band. Our search was conducted on the 48 OGLE II fields of the Galactic Bulge.This search has resulted in 29053 Be star candidates, 198 of them showing periodic light variations. Nearly 1500 stars in this final sample are almost certainly Be stars, providing an ideal sample for spectroscopic multiobject follow-up studies.

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arXiv2007

The pre-cataclysmic variable, LTT560

System parameters of the object LTT560 are determined in order to clarify its nature and evolutionary status. We apply time-series photometry to reveal orbital modulations of the light curve, time-series spectroscopy to measure radial velocities of features from both the primary and the secondary star, and flux-calibrated spectroscopy to derive temperatures of both components. We find that LTT560 is composed of a low temperature T~7500K DA white dwarf as the primary and an M5.5+-1 main-sequence star as the secondary component. The current orbital period is Porb=3.54(07)h. We derive a mass ratio Msec/Mwd = 0.36(03) and estimate the distance to d=25-40pc. Long-term variation of the orbital light curve and an additional H-alpha emission component on the white dwarf indicate activity in the system, probably in the form of flaring and/or accretion events.

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arXiv2007

K-band spectroscopy of pre-cataclysmic variables

We have taken K-band spectroscopy of a sample of 13 pre-CVs in order to examine them for anomalous chemical abundances. In particular, we study the strength of the 12CO and 13CO absorption bands that have been found diminished and enhanced, respectively, in similar studies of CVs. All our systems show CO abundances that are within the range observed for single stars. The weakest 12CO bands with respect to the spectral type are found in the pre-CV BPM 71214, although on a much smaller scale than observed in CVs. Furthermore there is no evidence for enhanced 13CO. Taking into account that our sample is subject to the present observational bias that favours the discovery of young pre-CVs with secondary stars of late spectral types, we can conclude the following: 1) our study provides observational proof that the CO anomalies discovered in certain CVs are not due to any material acquired during the common envelope phase, and 2) if the CO anomalies in certain CVs are not due to accretion of processed material during nova outburst, then the progenitors of these CVs are of a significantly different type than the currently known sample of pre-CVs.

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