CDROM/AJ/V110/P1649
Stellar Populations Near the M33 Nucleus
(Mighell+ 1995)
=========================================================================
=======
Hubble Space Telescope Planetary Camera Observations of the Stellar
Populations
Near the Nucleus of M33
Kenneth J. Mighell & R. Michael Rich
<1995, AJ, 110, 1649>
=1995AJ....110.1649M
=========================================================================
=======
Abstract:
We have studied the stellar populations near the nucleus of the nearby
spiral galaxy M33 using archival observations of the Hubble Space
Telescope Planetary Camera in the F555W and F785LP passbands. The I vs
(V-I) color-magnitude diagram reveals a young stellar population with a
blue main sequence and red supergiants, and stars in a blue loop that
are Cepheid candidates. An old red giant branch is clearly visible,
with a break at I = 20.7 mag which is, within the observational errors,
identical to the giant branch termination point of the Mould & Kristian
(1986, ApJ, 305, 591) halo field. However, red giants are seen up to I
= 19.5 mag, and many bright red giants are undetected in the V band.
We find evidence for a wide abundance spread of at least 1.5 dex from
metal-poor (~M15) to metal-rich (>= 47 Tucanae) in the Population II
stars, in sharp contrast to the M33 halo field of Mould & Kristian
(1986) which is metal-poor (~M92) with a narrow abundance range. We
show that the various stellar populations have different spatial
distributions. The Population II stars are more centrally concentrated
than the Population I stars. The red giants brighter than I = 20.7
(the termination point for a Galactic globular cluster giant branch)
are found to be more centrally concentrated than the (presumably) old
red giants. The most-centrally concentrated bright Population II
giants are probably associated with the many bright red giants that are
undetected in the V band. These infrared-bright giants were probably
created in an intermediate-age burst of star formation that took place
well after the formation of the oldest halo stars but long before the
recent burst of star formation seen in nearby OB associations. This
stellar population probably corresponds to the bulge identified in the
infrared H band by Minniti et al. (1993, ApJ, 410, L79).
File Summary:
------------------------------------------------------------------------------File Name
Lrecl
Records
Explanations
------------------------------------------------------------------------------table1.dat
70
4077
Photometry of stars near the nucleus of
M33
table1.fit
2880
60
FITS BINTABLE version of table 1
-------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
------------------------------------------------------------------------------Bytes Format Units
Label
Explanations
------------------------------------------------------------------------------1-10
I10
--ID
*Coded indentification
11-18
F8.2
mag
F785LP
F785LP (i) magnitude
19-24
F6.2
mag
e_F785LP
F785LP photometric error
25-32
F8.2
mag
F555W
F555W (v) magnitude
33-38
F6.2
mag
e_F555W
F555W photometric error
39-45
F7.2
mag
I
[]?=99.99 I magnitude
46-51
F6.2
mag
V-I
V-I color
52-59
F8.2
arcsec
dRA
*R.A. (J2000) offset from M33
nucleus
60-67
F8.2
arcsec
dDE
*Dec. (J2000) offset from M33
nucleus
68-70
I3
--Class
*Photometric measurement class
------------------------------------------------------------------------------Notes for file: table1.dat
------------------------------------------------------------------------------ID:
The left-most digit of the ID gives the PC chip number where the
star may be found (5, 6, 7, or 8). The right-most 4 digits of the ID
gives the x coordinate of the star multiplied by 10. The remaining
4 digits gives the y coordinate of the star multiplied by 10. All
positions are given with respect to the W0M00104T dataset. For
example, the first star in Table 1 has an ID of 505142912 which
indicates that it has the (x,y) position of (291.2, 51.4) on the PC5
CCD of the W0M00104T dataset.
dRA, dDE:
Offsets in arcseconds from the nucleus of M33 (ID = 634043615) for
the standard HST epoch of J2000.0.
Class:
1 = v and i photometry (2532 stars)
2 = only i photometry (1028 stars)
3 = only v photometry (517 stars)
------------------------------------------------------------------------------=========================================================================
=======
(End)
Lee Brotzman [ADS] 31Oct-1995