J/AJ/110/1649 VI photometry near the M33 nucleus (Mighell+ 1995)
Hubble Space Telescope Planetary Camera observations of the stellar populations
near the nucleus of M33
Mighell K.J., Rich R.M.
<Astron. J. 110, 1649 (1995)>
=1995AJ....110.1649M 1995AJ....110.1649M
ADC_Keywords: Populations, stellar ; Photometry
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=20.7mag which is, within the
observational errors, identical to the giant branch termination point
of the Mould & Kristian (1986ApJ...305..591M 1986ApJ...305..591M) halo field.
However, red giants are seen up to I=19.5mag, and many bright red
giants are undetected in the V band. We find evidence for a wide
abundance spread of at least 1.5dex from metal-poor (∼M15) to
metal-rich (≥47Tucanae) in the Population II stars, in sharp contrast
to the M33 halo field of Mould & Kristian (1986ApJ...305..591M 1986ApJ...305..591M) 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. (1993ApJ...410L..79M 1993ApJ...410L..79M).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 70 4077 Photometry of stars near the nucleus of M33
table1.fit 2880 60 FITS BINTABLE version of table 1
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See also:
J/AJ/121/861 : BVI photometry of central part of M33 (Macri+, 2001)
J/AJ/121/870 : Variables in the central part of M33 BVI phot. (Macri+, 2001)
J/A+A/366/498 : HST VI photometry of M33 star clusters (Chandar+, 2001)
J/AJ/110/2715 : UBV photometry in NGC 6822, M31 and M33 (Massey+ 1995)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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2- 10 I9 --- ID Coded identification (1)
12- 18 F7.2 mag F785LP F785LP (i) magnitude
20- 24 F5.2 mag e_F785LP F785LP photometric error
26- 32 F7.2 mag F555W F555W (v) magnitude
34- 38 F5.2 mag e_F555W F555W photometric error
40- 45 F6.2 mag Imag []?=99.99 I magnitude
47- 51 F5.2 mag V-I V-I color
53- 59 F7.2 arcsec dRA Right ascension (J2000) offset (2)
61- 67 F7.2 arcsec dDE Declination (J2000) offset (2)
69- 70 I2 --- Class Photometric measurement class (3)
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Note (1): 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 data set. 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 data set.
Note (2): Offsets in arcseconds from the nucleus of M33 (ID = 634043615) for
the standard HST epoch of J2000.0.
Note (3): 1 = v and i photometry (2532 stars)
2 = only i photometry (1028 stars)
3 = only v photometry (517 stars)
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Origin: AAS CD-ROM series, Volume 5, 1995 Lee Brotzman [ADS] 31-Oct-1995
(End) [CDS] 25-Jan-1996