With the grating spectrograph of the Bosque Alegre telescope, which gives a dispersion of 42 A/mm, the brightest stars of the galactic cluster IC 2391 were taken,for the purpose of radial velocity measurements and for a provisional spectral classification in the MK system.Asociación Argentina de Astronomí

Feinstein, Alejandro

Hernández, C.

English

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SPECTROSCOPIC OBSERVATIONS OF THE CLUSTER IC 2391 •
A.Feinstein and C .Hern&ndez 
(La Plata Observatory)
With the grating spectrograph of the Bosque Alegre telescope, 
which gives a dispersion of 1+2 A/mm, the brightest stars of the 
galactic cluster IC 2391 were taken,for the purpose of radial velo­
city measurements and for a provisional spectral classification in 
the MK system.
Two stars, namely N.2 and 6(HR 314+2 and HD 71+275^respectively) 
from Hoggfc list (i960) display radial velocity variations .The mean 
of the radial velocity of 11 stars gives V = +15,0 km/sec ±  2,1. 
Star number 32(HD 71+-536) according to Hogg* s color and proper motion 
perhaps does not pertain to the cluster. When leaving out this star, 
the ^ = 15,6 + 1,8 km/sec.
The most Interesting results of the spectral classification are 
the following: star N.I+ (HR 3I+-66) is a peculiar star of the SI-Al+200 
type; star N.ll (HD 7I+I69) is a metallic-line star being classified 
A2 according to hydrogen and A7 according to the metallic lines; 
star number 32, for which unfortunately we have only one plate also 
displays some peculiarities. The brightest stars of this cluster 
are of spectral type b 6 and d^/e^as judged by Its spectrum,would 
lie a little above the main sequence.
With our spectral types and luminosity classes and the intrin­
sic colors we obtain a color excess EB_V = -0^01 ± 0^01 end adopt 
thus = 0.00. The spectral types and the related absolute mag­
nitudes (Johnson and Iriarte,l958) give the modulus m-M=6T?8+o7o7 
(excluding star number 32), which gives a distance of 182 pc.
A discussion of the proper motions of the zone shows that the 
proper motion of the cluster obtained by Hogg is mainly the reflected 
solar motion.
The star HD 753»i+0 was classified by Jaschek and Jaschek (1959) 
as pertaining to the S1-AU200 group and is located at a distance of 2 ° 
from the center of the cluster. Its spectrum is practically Identical 
with the one of the cluster star N.Ij.. Prom the radial velocity (Vr = 
+l6,S km/sec) and the apparent visual magnitude (n^ = 5,96) it seems 
certain that HD 755^0 pertains also to the cluster,lying about 6 pc. 
away from the cluster center.
The cluster Is not associated with HII regions (Hogg,i960),but 
In the neighborhood (50*-and 5°) there are some (Abt, Morgan and 
Strflmgren, 1957» Gum,1956) which are excited by j  Vel and £ Pup, 
located at a distance of about 250 pc. As the cluster Is located at 
182 pc from us and the projected distance between the cluster and 
the cloud is 5» lt|re suits that IC 2391 is within the Str&mgren sphere 
produced by the two stars, which would explain the absence of HI and 
HII regions.
The age of the cluster found by Hogg (approximately 2 or lpclO^  
years) is not changed by the present results. Therefore this object 
Is one of the youngest clusters which contains peculiar stars.
The work will be extended to fainter stars.
Bibliography:
Abt, H.A.,Morgan W.W. and Str8mgren B. Ap.J. 126, 522, 1957. 
Gum,C.S. Memoirs of the Royal Astronomical Society. o7»155»1955. 
Gum,C.S. The Observatory, 76, 150, 1956.
Hogg,A.R. Publ. A.S.P. 72,8571960.
Jaschek M. and C.Jaschek7 Publ. A.S.P. 21,1*8, 1959.
Johnson,H.L. and B.Iriarte, Lowell Observatory,Bulletin 21, 1958.
15


Spectroscopic observations of the cluster IC 2391

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Spectroscopic observations of the cluster IC 2391

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