arXiv subjects

T. Zwitter

Publications and source records attributed to T. Zwitter.

136 records · Page 8Linked to original sources

arXiv2002

V838 Mon and the new class of stars erupting into cool supergiants (SECS)

V838 Mon has undergone one of the most mysterious stellar outbursts on record. The spectrum at maximum closely resembled a cool AGB star, evolving toward cooler temperatures with time, never reaching optically thin conditions or a nebular stage. The latest spectral type recorded is M8-9. The amplitude peaked at DeltaV=9 mag, with the outburst evolution being characterized by a fast rise, three maxima over four months, and a fast decay (possibly driven by dust condensation in the ejecta). BaII, LiI and s-element lines were prominent in the outburst spectra. Strong and wide (500 km/sec) P-Cyg profiles affected low ionization species, while Balmer lines emerged to modest emission only during the central phase of the outburst. A light-echo discovered expanding around the object constrains its distance to 790+/-30 pc, providing M_V=+4.45 in quiescence and M_V=-4.35 at optical maximum (dependent on the still uncertain E(B-V)=0.5 reddening). The visible progenitor resembled a somewhat under-luminous F0 main sequence star, that did not show detectable variability over the last half century. V838 Mon together with M31-RedVar and V4332 Sgr seems to define a new class of astronomical objects: stars that erupt into cool supergiants (SECS). They do not develop optically thin or nebular phases, and deep P-Cyg profiles denounce large mass loss at least in the early outburst phases. Their visible progenitors are located close to the Main Sequence, away from the post-AGB region. After the outburst, the remnants still closely resemble the precursors (same brightness, same spectral type). Many more similar objects could be buried among poorly studied novae that have been classified as Miras on the base of a single spectrum at maximum brightness.

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arXiv2002

The mysterious eruption of V838 Mon

V838 Mon is marking one of the most mysterious stellar outbursts on record. The spectral energy distribution of the progenitor resembles an under-luminous F main sequence star (at V=15.6 mag), that erupted into a cool supergiant following a complex and multi-maxima lightcurve (peaking at V=6.7 mag). The outburst spectrum show BaII, LiI and lines of several s-elements, with wide P-Cyg profiles and a moderate and retracing emission in the Balmer lines. A light-echo discovered expanding around the object helped to constrain the distance (d=790+/-30 pc), providing M_V=+4.45 in quiescence and M_V=-4.35 at optical maximum (somewhat dependent on the still uncertain E(B-V)=0.5 reddening). The general outburst trend is toward lower temperatures and larger luminosities, and continuing so at the time of writing. The object properties conflict with a classification within already existing categories: the progenitor was not on a post-AGB track and thus the similarities with the born-again AGB stars FG Sge, V605 Aql and Sakurai's object are limited to the cool giant spectrum at maximum; the cool spectrum, the moderate wind velocity (500 km/sec and progressively reducing) and the monotonic decreasing of the low ionization condition argues against a classical nova scenario. The closest similarity is with a star that erupted into an M-type supergiant discovered in M31 by Rich et al. (1989), that became however much brighter by peaking at M_V=-9.95, and with V4332 Sgr that too erupted into an M-type giant (Martini et al. 1999) and that attained a lower luminosity, closer to that of V838 Mon. M31-RedVar, V4332 Sgr and V838 Mon could be manifestations of the same and new class of astronomical objects.

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arXiv2001

Searching for the Physical Drivers of the Eigenvector 1 Correlation Space

[Latex markup removed] We recently discussed an Eigenvector 1 (E1) parameter space that provides optimal discrimination between the principal classes of broad-line Active Galactic Nuclei (AGN). In this paper we begin a search for the most important physical parameters that are likely to govern correlations and data point distribution in E1 space. We focus on the principal optical parameter plane involving the width of the H-beta broad component and the equivalent width ratio between the FeII blend at 4570 A and H-beta broad component. We show that the observed correlation for radio-quiet sources can be accounted for if it is primarily driven by the ratio of AGN luminosity to black hole mass (L/M proportional to Eddington ratio) convolved with source orientation. L/M apparently drives the radio-quiet correlation only for FWHM(H-beta) < 4000 km/s which includes Narrow Line Seyfert 1 (NLSy1) galaxies and can be said to define an AGN ``main sequence.'' Source orientation plays an increasingly important role as FWHM(H-beta) increases. We also argue that AGN lying outside the radio-quiet ``main sequence,'' and specifically those with optical FeII much stronger than expected for a given FWHM(H-beta), may all be Broad Absorption Line QSOs.

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arXiv2001

Evaluating GAIA performances on eclipsing binaries. I. Orbits and stellar parameters for V505 Per, V570 Per and OO Peg

The orbits and physical parameters of three detached, double-lined A-F eclipsing binaries have been derived combining H_P, V_T, B_T photometry from the Hipparcos/Tycho mission with 8500-8750 Ang ground-based spectroscopy, mimicking the photometric+spectroscopic observations that should be obtained by GAIA, the approved Cornerstone 6 mission by ESA. This study has two main objectives, namely (a) to derive reasonable orbits for a number of new eclipsing binaries and (b) to evaluate the expected performances by GAIA on eclipsing binaries and the accuracy achievable on the determination of fundamental stellar parameters like masses and radii. It is shown that a 1% precision in the basic stellar parameters can be achieved by GAIA on well observed detached eclipsing binaries provided that the spectroscopic observations are performed at high enough resolution. Other types of eclipsing binaries (including semi-detached and contact types) and different spectral types will be investigated in following papers along this series.

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arXiv2001

Discovery of a bipolar and highly variable mass outflow from the symbiotic binary StHa 190

A highly and rapidly variable bipolar mass outflow from StHa 190 has been discovered, the first time in a yellow symbiotic star. Permitted emission lines are flanked by symmetrical jet features and multi-component P-Cyg profiles, with velocities up to 300 km/sec. Given the high orbital inclination of the binary, if the jets leave the system nearly perpendicular to the orbital plane, the de-projected velocity equals or exceeds the escape velocity (1000 km/sec). StHa190 looks quite peculiar in many other respects: the hot component is an O-type sub-dwarf without an accretion disk or a veiling nebular continuum and the cool component is a G7 III star rotating at a spectacular 105 km/sec unseen by a large margin in field G giants.

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arXiv2000

Eigenvector 1: An Optimal Correlation Space for Active Galactic Nuclei

We identify a correlation space involving optical and UV emission line parameters as well as the soft X-ray spectral index that provides optimal discrimination between all principal classes of active galactic nuclei. Most of the sources in our three high quality data samples show a strong intercorrelation with narrow line Seyfert 1 (NLSy1) galaxies and steep spectrum radio galaxies occupying opposite extrema in the space. NLSy1 sources show a clear continuity with broader line sources indicating that they are not a disjoint class of AGN as is sometimes suggested. We interpret the principal intercorrelation in the parameter space as being driven by AGN luminosity to black hole mass ratio (L/M prop. to the Eddington ratio). Source orientation no doubt also plays an important role but it is not yet clear whether FWHM H beta or CIV 1549 line shift is the better indicator. We tentatively identify two RQ populations: an almost pure RQ population A with FWHM<=4000 and population B which occupies the same parameter domain as the flat spectrum RL sources. A possible interpretation sees Pop. A/NLSy1 as lower mass/high accretion rate sources and Pop. B/RL sources the opposite.

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arXiv2000

Spectroscopy and BVI photometry of the young open cluster NGC 6604

BVI photometry (from South Africa Astron. Obs.), Echelle high resolution spectroscopy and AFOSC integral field spectroscopy (from Asiago, Italy) of the young open cluster NGC 6604 are presented. Age, distance, reddening, membership, radial and rotational velocities are derived and discussed. An age of 5 million years, a distance of 1.7 kpc and a reddening E(B-V)=1.02 are found. The cluster radial velocity is in agreement with the Hron (1987) model for the Galaxy disk rotation. Pre-ZAMS objects are not present down to M_V = +1.5 mag.

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arXiv1999

The 1999 outburst of the eclipsing and recurrent nova U Scorpii

The spectroscopic and photometric evolution of the 1999 outburst of the eclipsing and recurrent nova U Sco is presented. The photometric evolution closely matches that of the previous events. The FWZI=10,000 km/sec for emission lines at maximum has decreased to 4000 km/sec by day +23, with continuous and dramatic changes in the line profiles. No nebular line has become visible and the ionization degree has increased during the brightness decline. A not previously reported and quite puzzling splitting of the emission lines into three components after the first two weeks is outstanding in our spectra. The radiated luminosity is found to be a tiny fraction of that of classical novae for any reasonable distance to U Sco.

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arXiv1997

On the Origin of Broad Fe K alpha and Hi H alpha Lines in AGN

We examine the properties of the Fe emission lines that arise near 6.4 keV in the ASCA spectra of AGN. Our emphasis is on the Seyfert 1 galaxies where broad and apparently complex Fe K alpha emission is observed. We consider various origins for the line but focus on the pros and cons for line emitting accretion disk models. We develop a simple model of an illuminated disk capable of producing both X-ray and optical lines from a disk. The model is able to reproduce the observed Fe K alpha FWHM ratio as well as the radii of maximum emissivity implied by the profile redshifts. The overall profile shapes however do not fit well the predictions of our disk illumination model nor do we derive always consistent disk inclinations for the two lines. We conclude that the evidence for and against an accretion disk origin for the Fe K alpha emission is equal at best. The bulk of the data requires a very disparate set of line fits which shed little light on a coherent physical model. We briefly consider alternatives to disk emission models and show that a simple bicone model can reproduce the FE line profiles equally well.

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arXiv1994

Pictor A: A New Double-Peaked Emission Line Quasar

We obtained a new spectrum for the radio galaxy Pictor~A in December 1993. Comparison with previous data obtained in 1983 and 1987 shows that the broad component of the Balmer lines has increased considerably in strength and complexity. The Balmer lines now show a boxy, double peaked profile with FWZI$\sim$24000 \kms. Although the 1993 H\a\ profile is reminiscent of Arp~102B, accretion disk models face immediate difficulty because (1) the redshifted peak in the profile is considerably stronger than the blue one, and (2) the red and blue peaks varied at different epochs. The latter finding strongly favors a predominance of radial motion. We argue that Pictor~A, and the rare objects with similar extremely broad emission line profiles, are better understood if the orientation is such that the gas is predominantly moving along the line of sight (i.e.\ a geometrical extremum).

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