Showing papers by "R. P. Kudritzki published in 2006"

The subdwarf B + white dwarf binary KPD 1930+2752 - a Supernova Type Ia progenitor candidate

Abstract: The nature of the progenitors of type Ia supernovae is still under controversial debate. KPD 1930+2752 is one of the best SN Ia progenitor candidates known today. The object is a double degenerate system consisting of a subluminous B star and a massive white dwarf. Maxted et al. 2000 conclude that the system mass exceeds the Chandrasekhar mass. This conclusion, however, rests on the assumption that the sdB mass is 0.5 Mo. However, recent binary population synthesis calculations suggest that the mass of an sdB star may range from 0.3 Mo to more than 0.7 Mo. It is therefore important to measure the mass of the sdB star simultaneously with that of the white dwarf. Since the rotation of the sdB star is tidally locked to the orbit the inclination of the system can be constrained. An analysis of the ellipsoidal variations in the light curve allows to tighten the constraints derived from spectroscopy. We derive the mass-radius relation for the sdB star from a quantitative spectral analysis. The projected rotational velocity is determined for the first time from high-resolution spectra. In addition a reanalysis of the published light curve is performed. The atmospheric and orbital parameters are measured with unprecedented accuracy. In particular the projected rotational velocity vrotsini = 92.3 +/- 1.5 km/s is determined. The mass of the sdB is limited between 0.45 Mo and 0.52 Mo. The total mass of the system ranges from 1.36 Mo to 1.48 Mo and hence is likely to exceed the Chandrasekhar mass. So KPD 1930+2752 qualifies as an excellent double degenerate supernova Ia progenitor candidate.

Faint supernovae and supernova impostors: case studies of SN 2002kg/NGC 2403-V37 and SN 2003gm

Abstract: Photometric and spectroscopic observations of the faint Supemovae (SNe) 2002kg and 2003gm, and their precursors, in NGC 2403 and NGC 5334 respectively, are presented The properties of these SNe are discussed in the context of previously proposed scenarios for faint SNe: low mass progenitors producing under-energetic SNe; SNe with ejecta constrained by a circumstellar medium; and outbursts of massive Luminous Blue Variables (LBVs) The last scenario has been referred to as “Type V SNe”, “SN impostors” or “fake SNe” The faint SN 2002kg reached a maximum brightness of MV = -9 6 , much fainter than nor­ mal type II SNe The precursor of SN 2002kg is confirmed to be, as shown in previous work, the LBV NGC2403-V37 Late time photometry of SN 2002kg shows it to be only 06 mag­ nitudes fainter at 500 days than at the epoch of discovery Two spectra of SN 2002kg, with an approximately 1 year interval between observations, show only minor differences Strong Fell lines are observed in the spectra of SN 2002kg, similar to both the LBV NGC2363-V1 and the type Iln SN 1995G The spectrum of SN 2002kg does show strong resolved [NII] at AA6549,6583 A The identified progenitor of SN 2003gm is a bright yellow star, consistent with a F5-G2 supergiant, similar to the identified progenitor of SN 2004et SN 2003gm, at the epoch of discovery, was of similar brightness to the possible fake SN 1997bs and the type IIP SNe 1999br and 2005cs Photometrically SN 2003gm shows the same decrease in bright­ ness, over the same time period as SN 1997bs The light curve and the spectral properties of SN 2003gm are also consistent with some intrinsically faint and low velocity type II SN The early time spectra of SN 2003gm are dominated by Balmer emission lines, which at the observed resolution, appear similar to SN 2000ch On the basis of the post-discovery photo­ metric and spectroscopic observations presented here we suggest that SN 2003gm is a similar event to SN 1997bs, although the SN/Lb V nature of both of these objects is debated At 226 days post-discovery the spectrum of SN 2003gm is strongle contaminated by HII region emis­ sion lines, and it cannot be confirmed that the precursor star has disappeared The presence of strong [NII] lines, near H a, is suggested as a possible means of identifying objects such as SN 2002kg/NGC2403-V37 as being LBVs - although not as a general classification criterion of all LBVs masquerading as SNe

Faint Supernovae and Supernova Impostors: Case studies of SN2002kg/NGC2403-V37 and SN 2003gm

Abstract: Photometric and spectroscopic observations of the faint Supernovae (SNe) 2002kg and 2003gm, and their precursors, in NGC 2403 and NGC 5334 respectively, are presented. The properties of these SNe are discussed in the context of previously proposed scenarios for faint SNe: low mass progenitors producing under-energetic SNe; SNe with ejecta constrained by a circumstellar medium; and outbursts of massive Luminous Blue Variables (LBVs). The last scenario has been referred to as ``Type V SNe'', ``SN impostors'' or ``fake SNe.'' The faint SN 2002kg reached a maximum brightness of $\mathrm{M_{V}=-9.6}$, much fainter than normal type II SNe. The precursor of SN 2002kg is confirmed to be, as shown in previous work, the LBV NGC2403-V37. Strong $\mathrm{Fe II}$ lines are observed in the spectra of SN 2002kg, similar to both the LBV NGC2363-V1 and the type IIn SN 1995G. The spectrum of SN 2002kg does show strong resolved $\mathrm{[N II]}$ at $\lambda\lambda$6549,6583\ang. The identified progenitor of SN 2003gm is a bright yellow star, consistent with a F5-G2 supergiant. SN 2003gm, at the epoch of discovery, was of similar brightness to the possible fake SN 1997bs. Photometrically SN 2003gm shows the same decrease in brightness, over the same time period as SN 1997bs. The early time spectra of SN 2003gm are dominated by Balmer emission lines, which at the observed resolution, appear similar to SN 2000ch. On the basis of the post-discovery photometric and spectroscopic observations presented here we suggest that SN 2003gm is a similar event to SN 1997bs. The presence of strong $\mathrm{[N II]}$ lines, near $\mathrm{H\alpha}$, is suggested as a possible means of identifying objects such as SN 2002kg/NGC2403-V37 as being LBVs - although not as a general classification criterion of all LBVs masquerading as SNe (abridged).

The ARAUCARIA Project - First Observations of Blue Supergiants in NGC 3109

Abstract: NGC 3109 is an irregular galaxy at the edge of the Local Group at a distance of 1.3 Mpc. Here we present new VLT observations of its young, massive star population, which have allowed us to probe stellar abundances and kinematics for the first time. The mean oxygen abundance obtained from early B-type supergiants confirms suggestions that NGC 3109 is very metal poor. In this context we advocate studies of the stellar population of NGC 3109 as a compelling target for future Extremely Large Telescopes (ELTs).