Subject: Poster abstract

From: [email-masked]
Date: Wed, 09 Aug 1995 19:17:32 +0200

ON THE POSSIBLE CONTRIBUTION OF dK AND dM STARS TO THE TOTAL MASS OF 
STAR CLUSTERS

G. SZECSENYI-NAGY

Department of Astronomy
Eotvos Lorand University
Budapest, VIII. Ludovika ter 2.
H-1083 HUNGARY

ABSTRACT

dK and dM class stars or red dwarfs are intrinsically faint and cool objects and
this explains why these abundant celestial bodies have remained undiscovered for
such a long time. Visual observers of the pre-photographic era were able to list
only a handful of this species and even the shockingly fruitful technique of 
astronomical photography had not been too productive in this field of astronomy,
since the photosensitive layers of the early photographic plates were not sensi-
tive in the yellow-red range of the spectrum. Each of the red dwarfs registered
before the use of modern astrophotographic equipments (fast cameras and plates 
of enhanced {red} sensitivity) belonged to the immediate vicinity of the sun. It
means that only those stars had been detected and located which were not farther
than about 5 pc. However they turned out to be the most common of the stars soon
as methods of distance determination evolved and a reliable sample of the solar
neighbourhood could be compiled. The next step arrived with the invention of the
Schmidt optical system, which offered the possibility of the detection of very
faint stars in unprecedently wide regions of the sky simultaneously. We learned
that these faint sources fill the volume of open clusters and other stellar 
groups too. The discovery of flare stars (a subclass of red dwarfs) offered a
very effective tool for collecting more and more data about the dK/dM population
of stellar systems. Applying some of the basic equations of statistics we were
able to demonstrate that the traditional methods had never allowed the detection
of very faint and red members of the clusters. Optical and NIR observations of
these objects during the last decades allowed to estimate statistically the most
probable number and percentage of the red dwarf population. It turned out to be
in the 65-80 % range i.e. the absolute majority of the stars in star clusters as
well as in the solar vicinity belong to the red dwarf class. Stellar populations
of significantly more distant regions can not be investigated making use of the
conventional methods but the state of the art telescopes, detectors and methods
open new doors of the cosmos. The capacity of some of the best devices in the
extension of these studies to the distance range of the globular clusters of the
Milky Way and even the Magellanic Clouds will be discussed to finish with. 

This study was supported by NSRF of Hungary Grant No. OTKA-T007595.