J/MNRAS/396/1231 Astrophotometric catalogue of NGC 891 (Rejkuba+, 2009)
The stellar population content of the thick disc and halo of the Milky Way
analogue NGC 891.
Rejkuba M., Mouhcine M., Ibata R.
<Mon. Not. R. Astron. Soc., 396, 1231-1246 (2009)>
=2009MNRAS.396.1231R 2009MNRAS.396.1231R
ADC_Keywords: Galaxies, nearby ; Photometry, HST ; Morphology
Keywords: galaxies: formation - galaxies: haloes -
galaxies: individual: NGC 891 - galaxies: stellar content
Abstract:
We present deep VI images obtained with the Advanced Camera for
Surveys on board the Hubble Space Telescope, covering three fields in
the north-east side of the edge-on disc galaxy NGC 891. The observed
fields span a wide range of galactocentric distances along the eastern
minor axis, extending from the plane of the disc to 12kpc, and out to
∼25kpc along the major axis. The photometry of individual stars
reaches ∼2.5mag below the tip of the red giant branch. We use the
astrophotometric catalogue to probe the stellar content and
metallicity distribution across the thick disc and spheroid of
NGC 891.
Description:
Observations of three fields (H1, H2 and H3) along the eastern edge of
NGC 891 disc have been taken in 2003 February with the wide field
camera (WFC) of ACS as part of program GO-9414.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 67 18 The observing log
table2.dat 93 376320 Astrophotometric catalogue
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Name Field name
22- 23 I2 h RAh Right ascension (J2000)
25- 26 I2 min RAm Right ascension (J2000)
28- 32 F5.2 s RAs Right ascension (J2000)
34 A1 --- DE- Declination sign (J2000)
35- 36 I2 deg DEd Declination (J2000)
38- 39 I2 arcmin DEm Declination (J2000)
41- 44 F4.1 arcsec DEs Declination (J2000)
46- 55 A10 "YYYY-MM-DD" Date Observation date
57- 61 A5 --- Filter Filter (F606W or F814W)
63- 67 A5 s ExpTime Exposure time
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- ID Sequential number
8- 16 F9.6 deg RAdeg Right ascension in decimal degrees (J2000)
19- 27 F9.6 deg DEdeg Declination in decimal degrees (J2000)
29- 34 F6.3 mag Vmag V magnitude (1)
36- 40 F5.3 mag e_Vmag rms uncertainty on Vmag (1)
42- 47 F6.3 mag Imag I magnitude (1)
49- 53 F5.3 mag e_Imag rms uncertainty on Imag (1)
55- 58 F4.2 --- chi Chi value of the PSF fit (good if chi≤1.5)
60- 65 F6.1 --- S/N Signal-to-noise ratio
67- 72 F6.3 --- Sharp Sharpness parameter [-0.3/0.3 is good] (4)
74- 78 F5.3 --- Round Roundness parameter (4)
80- 84 F5.3 mag Crowd Crowding parameter (4)
86 I1 --- Type [1/2] Object type (2)
88- 89 I2 --- Field [1/32] Field (H1, H2, H3 or overlap 12 or 23)
91 I1 --- f_Vmag [0/7] Bad or saturated pixels in V (3)
93 I1 --- f_Imag [0/7] Bad or saturated pixels in I (3)
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Note (1): Calibrated V and I-band magnitudes and the associated errors as
computed by DOLPHOT, but multiplied by a factor of 1.6 to correct for
the underestimated dolphot errors
Note (2): Types 1,2 correspond to a stellar (point source) object:
1 = good star, 2 = star too faint for PSF determination.
Note (3): These last flags give an indication of whether a given star had
some bad or saturated pixels within the PSF fitting radius [see the
DOLPHOT manual by Dolphin (2005, DOLPHOT User's Guide for details:
http://purcell.as.arizona.edu/dolphot/dolphot.ps.gz)]:
1 = photometry aperture extends off chip
2 = too many bad or saturated pixels
4 = saturated at center of star
Note (4): DOLPHOT output parameters (from DOLPHOT User's Guide):
* Sharpness is 0 for a perfect stellar fit,
>0 if too sharp (e.g. a cosmic ray),
<0 if too broad (e.g. a cluster or galaxy)
* Roundness can be used to discriminate between extended objects
and diffraction spikes
* Crowding tells how much brighter the star would have been measured
had nearby stars not been fit simultaneously. It is 0 for an
isolated star.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 29-Oct-2009