arXiv subjects

M. Schultheis

Publications and source records attributed to M. Schultheis.

133 records · Page 8Linked to original sources

arXiv2001

Mass-Losing Semiregular Variable Stars in Baade's Windows

By cross-correlating the results of two recent large-scale surveys, the general properties of a well defined sample of semi-regular variable stars have been determined. ISOGAL mid-infrared photometry and MACHO lightcurves are assembled for approximately 300 stars in the Baade's Windows of low extinction towards the Galactic bulge. These stars are mainly giants of late M spectral type, evolving along the asymptotic giant branch (AGB). They are found to possess a wide and continuous distribution of pulsation periods and to obey an approximate log~period -- bolometric magnitude relation or set of such relations. Approximate mass-loss rates in the range of 1e-8 to 5e-7 M_sun per year are derived from ISOGAL mid-infrared photometry and models of stellar spectra adjusted for the presence of optically-thin circumstellar silicate dust. Mass-loss rates depend on luminosity and pulsation period. Some stars lose mass as rapidly as short-period Miras but do not show Mira-like amplitudes. A period of 70 days or longer is a necessary but not a sufficient condition for mass loss to occur. For AGB stars in the mass-loss ranges that we observe, the functional dependence of mass-loss rate on temperature and luminosity is found to be in agreement with recent theoretical predictions. If we include our mass-loss rates with a sample of extreme mass-losing AGB stars in the Large Magellanic Cloud, we get the general result for AGB stars that mass-loss rate is proportional to luminosity^{2.7}, valid for AGB stars with 10^{-8} to 10^{-4} M_sun per year (Abridged).

astro-ph↗

arXiv1999

Interstellar extinction towards the inner Galactic Bulge

DENIS observations in the J (1.2 micron) and K_S (2.15 micron) bands together with isochrones calculated for the RGB and AGB phase are used to draw an extinction map of the inner Galactic Bulge. The uncertainty in this method is mainly limited by the optical depth of the Bulge itself. A comparison with fields of known extinction shows a very good agreement. We present an extinction map for the inner Galactic Bulge (approx. 20 sq. deg.)

astro-ph↗

arXiv1999

ISOGAL-DENIS detection of red giants with weak mass loss in the Galactic Bulge

The ISOGAL project is a survey of the stellar populations, structure, and recent star formation history of the inner disk and bulge of the Galaxy. ISOGAL combines 15 and 7micron ISOCAM observations with DENIS IJKs data to determine the nature of a source and the interstellar extinction. In this paper we report an ISOGAL study of a small field in the inner Galactic Bulge (l=0deg, b=1.0deg, area=0.035 sq. deg) as a prototype of the larger area ISOGAL survey of the inner Galaxy. The five wavelengths of ISOGAL+DENIS, together with the relatively low and constant extinction in front of this specific field, allow reliable determination of the nature of the sources. The primary scientific result of this paper is evidence that the most numerous class of ISOGAL 15micron sources are Red Giants in the Galactic bulge and central disk, with luminosities just above or close to the RGB tip and weak mass-loss rates. They form loose sequences in the magnitude-colour diagrams [15]/Ks-[15] and [15]/[7]-[15]. Their large excesses at 15micron with respect to 2micron and 7micron is due to circumstellar dust produced by mass-loss at low rates. These ISOGAL results are the first systematic evidence and study of dust emission at this early stage (''Intermediate'' AGB), before the onset of the large mass-loss phase. It is thus well established that efficient dust formation is already associated with such low mass-loss rates during this early phase.

astro-ph↗

arXiv1999

ISOGAL Survey of Baade's Windows in the Mid-infrared

The ISOGAL mid-infrared survey of areas close to the Galactic Plane aims to determine their stellar content and its possible bearing on the history of the Galaxy. The NGC6522 and Sgr I Baade's Windows of low obscuration towards the inner parts of the Bulge represent ideal places in which to calibrate and understand the ISOGAL colour-magnitude diagrams. The survey observations were made with the ISOCAM instrument of the ISO satellite. The filter bands chosen were LW2(~7 microns) and LW3(~15 microns). The results presented here show that most of the detected objects are late M-type giants on the AGB, with a cut-off for those earlier than M3-M4. The most luminous members of these two Bulge fields at 7 microns are the Mira variables. However, it is evident that they represent the end of a sequence of increasing 15 micron dust emission which commences with M giants of earlier sub-type. In observations of late-type giants the ISOCAM 15 micron band is mainly sensitive to the cool silicate or aluminate dust shells which overwhelm the photospheric emission. However, in ordinary M-giant stars, the 7 micron band is not strongly affected by dust emission and may be influenced instead by absorption. The nu2 band of water at 6.25 microns and the SiO fundamental at 7.9 microns are likely contribitors to this effect. A group of late M stars has been found which vary little or not at all but have infrared colours typical of well-developed dust shells. Their luminosities are similar to those of 200-300 day Miras but they have slightly redder [7]-[15] colours which form an extension of the ordinary M giant sequence. The Mira dust shells show a mid-infrared [7]-[15] colour-period relation. ca 700 days.

astro-ph↗

arXiv1998

Field #3 of the Palomar-Groningen Survey II. Near-infrared photometry of semiregular variables

Near-infrared photometry (JHKL'M) was obtained for 78 semiregular variables (SRVs) in field #3 of the Palomar-Groningen survey (PG3, l=0, b=-10). Together with a sample of Miras in this field a comparison is made with a sample of field SRVs and Miras. The PG3 SRVs form a sequence (period-luminosity & period-colour) with the PG3 Miras, in which the SRVs are the short period extension to the Miras. The field and PG3 Miras follow the same P/(J--K)o relation, while this is not the case for the field and PG3 SRVs. Both the PG3 SRVs and Miras follow the SgrI period-luminosity relation adopted from Glass et al. (1995, MNRAS 273, 383). They are likely pulsating in the fundamental mode and have metallicities spanning the range from intermediate to approximately solar.

astro-ph↗

arXiv1998

Mixed Early and Late-Type Properties in the Bar of NGC 6221: Evidence for Evolution along the Hubble Sequence?

Rotation curves and velocity dispersion profiles are presented for both the stellar and gaseous components along five different position angles (P.A.=5, 50, 95, 125 and 155 degrees) of the nearby barred spiral NGC 6221. The observed kinematics extends out to about 80" from the nucleus. Narrow and broad-band imaging is also presented. The radial profiles of the fluxes ratio [NII]/Halpha reveal the presence of a ring-like structure of ionized gas, with a radius of about 9" and a deprojected circular velocity of about 280 km/s. The analysis of the dynamics of the bar indicates this ring is related to the presence of an inner Lindblad resonance (ILR) at 1.3 kpc. NGC6221 is found to exhibit intermediate properties between those of the early-type barred galaxies: the presence of a gaseous ring at an ILR, the bar edge located between the ILR's and the corotation radius beyond the steep rising portion of the rotation curve, the dust-lane pattern, and those of the late-type galaxies: an almost exponential surface brightness profile, the presence of Halpha regions along all the bar, the spiral-arm pattern. It is consistent with scenarios of bar-induced evolution from later to earlier-type galaxies.

astro-ph↗

arXiv1996

Field #3 of the Palomar-Groningen Survey I. Variable stars at the edge of the Sagittarius dwarf galaxy

A catalogue is presented with variable (RR Lyrae, semiregular and Mira) stars located inside field #3 of the Palomar-Groningen Survey, at the outer edge of the Sagittarius dwarf galaxy. One of the semiregular variables is a carbon star, comparable with those found by Azzopardi et al. (1991). Serendipity provides the suggestion, that their carbon stars might not be located inside, but behind the bulge in the Sagittarius dwarf galaxy.

astro-ph↗