J/A+A/419/149 UBV(I)c photometry of NGC 6996 (Villanova+, 2004)
Optical photometry and spectral classification in the field of the open cluster
NGC 6996 in the North America Nebula.
Villanova S., Baume G., Carraro G., Geminale A.
<Astron. Astrophys., 419, 149-159 (2004)>
=2004A&A...419..149V 2004A&A...419..149V
ADC_Keywords: Clusters, open ; Photometry, UBVRI
Keywords: Galaxy: open clusters and associations: individual: NGC 6996 -
Galaxy: open clusters and associations: general -
Abstract:
We present and discuss broad band CCD UBV(I)c photometry and low
resolution spectroscopy for stars in the region of the open cluster
NGC 6996, located in the North America Nebula. The new data allow us
to tightly constrain the basic properties of this object. We revise
the cluster size, which in the past has been significantly
underestimated. The width of the Main Sequence is mainly interpreted
in terms of differential reddening, and indeed the stars' color
excess E(B-V) ranges from 0.43 to 0.65, implying the presence of a
significant and evenly distributed dust component. We cross-correlate
our optical photometry with near infrared photometry from 2MASS, and
by means of spectral classification we are able to build extinction
curves for an handful of bright members. We find that the reddening
slope and the total to selective absorption ratio Rv toward NGC 6996
are anomalous. Moreover the reddening-corrected colors and magnitudes
allow us to derive estimates for the cluster distance and age, which
turn out to be 760±70pc (V0-MV=9.4±0.2) and ∼350Myr, respectively.
Based on our results, we suggest that NGC 6996 is located in front of
the North America Nebula, and does not seem to have any apparent
relationship with it.
Description:
CCD UBV(I)c data were obtained during three observational runs. Two
of them were carried out with the AFOSC camera at the 1.82m Copernico
telescope of Cima Ekar (Asiago, Italy), on the photometric nights of
November 8, 2002 and September 18, 2003. The other run was conducted
at Teramo Observatory (Italy) using a 512x512 CCD onboard the 0.72m
Teramo Normale Telescope (TNT), on December 5, 2002.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 207 2699 Photometric catalogue of the NGC 6996 region
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/259 : The Tycho-2 Catalogue (Hog+ 2000)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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5- 8 I4 --- Seq Identification number (this work)
15- 17 A3 --- ZS Numbering from Zdanavicius & Straizys,
1990Ap&SS.173..309Z 1990Ap&SS.173..309Z, Cl* NGC 6996 ZS NN (1)
21- 26 F6.1 pix Xpos X position in arcseconds (2)
30- 35 F6.1 pix Ypos Y position in arcseconds (2)
39- 40 I2 h RAh Right Ascension (J2000)
42- 43 I2 min RAm Right Ascension (J2000)
45- 48 F4.1 s RAs Right Ascension (J2000)
51 A1 --- DE- Declination sign (J2000)
52- 53 I2 deg DEd Declination (J2000)
55- 56 I2 arcmin DEm Declination (J2000)
58- 61 F4.1 arcsec DEs Declination (J2000)
66- 70 F5.2 mag Vmag V magnitude
72- 73 A2 --- u_Vmag [: ] Comments for V magnitude (3)
78- 82 F5.2 mag B-V ? B-V colour index
84- 85 A2 --- u_B-V [: ] Comments for B-V index (3)
90- 94 F5.2 mag U-B ? U-B colour index
96- 97 A2 --- u_U-B [: ] Comments for U-B index (3)
102-106 F5.2 mag V-Ic ? V-Ic colour index
108-109 A2 --- u_V-Ic [: ] Comments for V-Ic index (3)
111-112 A2 --- Memb Membership assignment (4)
123-127 F5.2 mag E(B-V) ? B-V colour excess
132-136 F5.2 mag E(U-B) ? U-B colour excess
141-145 F5.2 mag E(V-I) ? V-Ic colour excess
147-152 A6 --- SpType Spectral Classification
156-171 A16 --- 2MASS 2MASS identification (Cat. II/246)
175-177 A3 --- --- TYCHO-2 identification
179-190 A12 --- TYC TYCHO-2 identification (Cat. I/259)
193-208 A16 --- OtherID BD, BSC and/or GSC identification
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Note (1): Stars separated in two components are identified as 'a' and 'b'
Note (2): Adopted center: 20:56:30+44:38:00 (J2000)
Note (3): Comments on photometry:
(: ) error larger than 0.05
(::) error larger than 0.10
Note (4): Membership assignment:
lm = likely member
pm = probable member
nm = non-member
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Acknowledgements: Gustavo L. Baume
(End) Patricia Bauer [CDS] 24-May-2004