J/A+A/341/98 The ionizing cluster of 30 Doradus. I. (Selman+ 1999)
The ionizing cluster of 30 Doradus. I. Internal reddening from NTT photometry.
Selman F., Melnick J., Bosch G., Terlevich R.
<Astron. Astrophys. 341, 98 (1999)>
=1999A&A...341...98S 1999A&A...341...98S
ADC_Keywords: Clusters, open ; Photometry, UBV
Keywords: stars: early-type - stars: luminosity function, mass function -
ISM: dust, extinction - galaxies: Magellanic Clouds -
Galaxy: open clusters and associations: general
Abstract:
UBV profile fitting photometry is presented for 1469 stars within
90arcsec of the center of the ionizing cluster of 30 Doradus
(NGC 2070). A value of 0.82±0.03 is found for the extinction
parameter S=E(U-B)/E(B-V), constant over almost the whole area covered
by this research, with some evidence for local variations. Two
reddening components can be identified: a smooth and moderate one that
increases towards R136, and a clumpy one varying widely across the
face of the cluster. The total-to-selective extinction parameter,
RV= AV/E(B-V), is found to be in the range of 3.0 to 3.7,
consistent with previous determinations. A new visualization tool, the
colour-magnitude stereogram, is introduced and used to argue that: (1)
the observations imply mass segregation in a dust filled cluster; (2)
that there has been continuous dust formation near the cluster core up
to the present; and (3) that an insidious systematic error has plagued
previous determinations of IMF slopes. A method to obtain an unbiased
estimate of the slope is discussed.
Astrometric calibration (from B. Skiff):
The source images were taken with the ESO NTT 3.6-meter telescope,
with a CCD detector at an image scale of 0.13arcsec/pixel in about
0.8arcsec seeing. Positions were determined via a reference net of
26 relatively bright and isolated stars in the region appearing in
either UCAC2 (Cat. I/289) or 2MASS (Cat. II/246). The x,y coordinates
were transformed using a quadratic least-squares fit; the rms
residuals using all the reference stars were 0.50 pixels in RA,
and 0.55 pixels in Dec, i.e. 0.097arcsec total.
A similar re-reduction of the survey by Parker (1993AJ....106..560P 1993AJ....106..560P),
which overlaps this one, shows that the Selman linkages with Parker
stars (column 'P93') are incomplete and contain some errors. Some of
these result from the relatively small image scale (0.49arcsec/pixel)
and poor seeing (1.2-2.0arcsec) of Parker's data, such that a single
Parker star is sometimes resolved into multiple components by Selman.
Among bright stars (V ≲ 15) that have been observed for spectral type
there are few such errors in the match-up. But among Parker's fainter
entries (V ≳ 17) are numerous false detections (clumps in nebulosity)
that are incorrectly linked by Selman with true stars a couple of
arcseconds from Parker's non-stellar objects.
Objects:
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RA (2000) DE Designation(s)
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05 38 42.8 -69 06 03 RMC 136 = HD 38268 = 30 Dor
05 38 42. -69 05 30 NGC 2070
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 106 1469 UBV photometry of NGC 2070 star members
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See also:
II/187 : 30 Doradus OB Associations (Parker 1992)
J/AJ/107/1054 : 30 Dor region UBV photometry (Malumuth+, 1994)
J/ApJ/413/604 : 30 Dor UV and optical photometry (Hill+, 1993)
J/A+A/443/851 : Effective temperature of 30 Dor population (Selman+, 2005)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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2- 5 I4 --- Seq Star number
9- 10 I2 h RAh Right Ascension J2000 (hours) (1)
12- 13 I2 min RAm Right Ascension J2000 (minutes) (1)
15- 20 F6.3 s RAs Right Ascension J2000 (seconds) (1)
22 A1 --- DE- Declination J2000 (sign) (1)
23- 24 I2 deg DEd Declination J2000 (degrees) (1)
26- 27 I2 arcmin DEm Declination J2000 (minutes) (1)
29- 33 F5.2 arcsec DEs Declination J2000 (seconds) (1)
36- 41 F6.1 pix xpos X coordinate (2)
43- 48 F6.1 pix ypos Y coordinate (2)
50- 54 I5 --- P93 ?=-1 Id in Parker's catalogue (3)
58- 63 F6.3 mag Vmag Apparent V magnitude
65- 69 F5.3 mag e_Vmag Error in apparent V magnitude
74- 79 F6.3 mag Bmag Apparent B magnitude
81- 85 F5.3 mag e_Bmag Error in apparent B magnitude
89- 94 F6.3 mag Umag Apparent U magnitude
96-100 F5.3 mag e_Umag Error in apparent U magnitude
104-106 F3.1 --- Chi2 Chi2 parameter from IRAF/DAOPHOT II
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Note (1): astrometric solution by B. Skiff, see the
"Astrometric calibration" section above.
Note (2):
x axis East to West, y axis South to North, scale of 0.13arcsec/pix;
R136 (J2000 position = 05:38:42.8-69:06:03) is located at
(x,y) = (456.4,432.3).
Note (3):
A -1 in this column indicates no match with the catalogue of Parker
(1993AJ....106..560P 1993AJ....106..560P, Cat. II/187). A negative Parker number
(smaller than -1) indicates that the star has spectroscopy.
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Acknowledgements:
Fernando J. Selman <fselman(at)sc6.sc.eso.org>
History:
* 18-Dec-1998: Original version with X and Y positions, prepared by
Fernando J. Selman [ESO] and Patricia Bauer [CDS]
* 04-Mar-2008: Addition of positions from B. Skiff (Lowell Obs.)
(End) Fernando J. Selman [ESO], Patricia Bauer [CDS] Brian Skiff 04-Mar-2008