Subject: [IAU 174 abstract 10 ]

From: iau174
Date: Thu, 10 Aug 95 22:26:35 JST

>From [email-masked]  Thu Aug 10 22:23:44 1995
Sender: [email-masked]
Date: Thu, 10 Aug 1995 15:14:32 +0200
From: [email-masked]
To: [email-masked]
Cc: [email-masked]
Subject: abstract (final version)

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 had extremely
low QE in the yellow-red band 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 filled 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 the faintest (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. Their contribution 
to the total membership is at least 65 % and more probably about three quarters.
Consequently the absolute majority of the stars in star clusters, associations 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 up new vistas to the universe. The capacity of the most prospective devices 
and sophisticated methods in the possible extension of these studies into the 
distance range of the globular clusters of the Milky Way and even the Magellanic 
Clouds will also be discussed. 

This study was supported by NSRF of Hungary Grant No. OTKA-T 7595.