# Variable and Multiple Stars in Hipparcos

Is there any way I can tell from Hipparcos catalog which stars are Binary/Multiple Stars and which are Variable stars?

Yes. If you have the Hipparcos data from ftp (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=I/239&-to=3), you will have several data files.

In hip_main.dat you have a field MultFlag at position 347 that indicates whether the star is a double or multiple star:

Note on MultFlag: indicates that further details are given in the Double
and Multiple Systems Annex:
C : solutions for the components
G : acceleration or higher order terms
O : orbital solutions
V : variability-induced movers (apparent motion arises from variability)
X : stochastic solution (probably astrometric binaries with short period)


To determine whether the star is a double or multiple star system, look in one of the files for double star solutions. For instance in h_dm_com.dat there is a field at bytes 24-25 that gives the number of components (2 for double and >2 for multiple stars).

24- 25  I2     ---     Ncomp    Number of components in this solution   (DCM2)


The Hipparcos number identifying the star can be found in bytes 43-48.

Of course this only works for multiple stars with orbital solutions.

For variability, three fields are provided in the main Hipparcos file:

314-320  F7.2  d       Period    ? Variability period (days)              (H51)
322  A1    ---     HvarType *[CDMPRU]? variability type               (H52)


with two notes (NB. if HvarType is C then the star is constant, i.e. not variable!):

Note on HvarType: Hipparcos-defined type of variability (a blank entry
signifies that the entry could not be classified as variable or constant):
C : no variability detected ("constant")
D : duplicity-induced variability
M : possibly micro-variable (amplitude < 0.03mag)
P : periodic variable
R : V-I colour index was revised due to variability analysis
U : unsolved variable which does not fall in the other categories
Note on moreVar: more data about periodic variability are provided


There are two additional files on variability: hip_va_1.dat and hip_va_2.dat, which provide information such as variable type (GCVS) and max and min magnitude and also the variable star name. You can find a description of the variable type in the General Catalogue of Variable Stars (GCVS) in the file vartype.txt if you download the GCVS at http://cdsarc.u-strasbg.fr/viz-bin/Cat?B/gcvs

• Meant to add Variable stars as well, is that available from hipparcos? – MiscellaneousUser Apr 17 '15 at 12:51
• What is meant by Orbital Solutions? – MiscellaneousUser Apr 17 '15 at 13:03
• Yes on variable stars, see my edit of the answer. – Dieudonné Apr 17 '15 at 13:06
• Orbital solutions are used to calculate the orbit of one star in the binary with respect to the other star. They can be found in the file 'hip_dm_o.dat'. – Dieudonné Apr 17 '15 at 13:09