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J/A+A/436/853      IR photometry of Alpha Per low-mass members   (Lodieu+, 2005)

A near-infrared survey for new low-mass members in Alpha Per. Lodieu N., McCaughrean M.J., Barrado y Navascues D., Bouvier J., Stauffer J.R. <Astron. Astrophys. 436, 853 (2005)> =2005A&A...436..853L
ADC_Keywords: Clusters, open ; Photometry, CCD ; Photometry, infrared Keywords: stars: low-mass, brown dwarfs - techniques: photometry - techniques: spectroscopy - infrared: stars - stars: Hertzsprung-Russell (HR) and C-M diagrams - open clusters and associations: individual : alpha Persei Abstract: We present a near-infrared (K'-band) survey of 0.7 square degree area in the α Persei open cluster (age=90Myr, distance=182pc) carried out with the Omega-Prime camera on the Calar Alto 3.5-m telescope. Combining optical data (Rc and Ic) obtained with the KPNO/MOSA detector and presented in Stauffer et al. (1999ApJ...527..219S; S99) with the K' observations, a sample of new candidate members has been extracted from the optical-infrared colour-magnitude diagram. The location of these candidates in the colour-colour diagram suggests that two-thirds of them are actually reddened background giants. About 20 new candidate members with masses between 0.3 and 0.04M are added to the ∼400 known Alpha Per cluster members. If they are indeed Alpha Per members, four of the new candidates would be brown dwarfs. We discuss the advantages and drawbacks of the near-infrared survey as compared to the optical selection method. We also describe the outcome of optical spectroscopy obtained with the Twin spectrograph on the Calar Alto 3.5-m telescope for about 30 candidates, including selected members from the optical sample presented in Barrado y Navascues et al. (2002, Cat. J/A+A/395/813) and from our joint optical/infrared catalogue. These results argue in favour of the optical selection method for this particular cluster. Description: Optical detections in five different fields of view (A, C, E, K, and L) are matched with the near-infrared detections described in this paper. The central coordinates of the five optical fields-of-view are as follows: (see Stauffer et al. 1999ApJ...527..219S for more details): A : RA = 03:27:10.0 DE = +49:24:00.0 C : RA = 03:24:50.0 DE = +48:42:00.0 E : RA = 03:19:35.0 DE = +49:27:00.0 K : RA = 03:27:00.0 DE = +50:13:00.0 L : RA = 03:23:10.0 DE = +48:11:00.0 The objects matched between the optical and the near-infrared catalogues are gathered in table2.dat. Optical and near-infrared coordinates (J2000.0) are provided as well as magnitudes and their associated errors. The last column give the name of the object according to the IAU convention. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 116 22129 Matched objects between the optical (Stauffer et al. (1999ApJ...527..219S, S99) and the near-infrared catalogue
See also: J/A+A/395/813 : Alpha Per faint stars photometry (Barrado y Navascues+, 2002) J/A+A/416/125 : RI photometry in alpha Per and Pleiades (Deacon+, 2004) J/AN/319/201 : Alpha Per cluster low-mass members. I. (Prosser+, 1998) J/AN/319/215 : Alpha Per cluster low-mass members. II. (Prosser+, 1998) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 5 I5 --- Seq Identification number 7- 8 I2 h RAh Optical Right ascension (J2000.0) 10- 11 I2 min RAm Optical Right ascension (J2000.0) 13- 17 F5.2 s RAs Optical Right ascension (J2000.0) 19 A1 --- DE- Optical Declination sign (J2000.0) 20- 21 I2 deg DEd Optical Declination (J2000.0) 23- 24 I2 arcmin DEm Optical Declination (J2000.0) 26- 29 F4.1 arcsec DEs Optical Declination (J2000.0) 31- 32 I2 h RAIh Near-infrared Right ascension (J2000.0) 34- 35 I2 min RAIm Near-infrared Right ascension (J2000.0) 37- 41 F5.2 s RAIs Near-infrared Right ascension (J2000.0) 43 A1 --- DEI- Near-infrared Declination sign (J2000.0) 44- 45 I2 deg DEId Near-infrared Declination (J2000.0) 47- 48 I2 arcmin DEIm Near-infrared Declination (J2000.0) 50- 53 F4.1 arcsec DEIs Near-infrared Declination (J2000.0) 55- 60 F6.3 mag K'mag K' magnitude 62- 66 F5.3 mag e_K'mag Error on the K' magnitude 68- 73 F6.3 mag Rcmag R_c magnitude from KPNO/MOSA (S99) 75- 79 F5.3 mag e_Rcmag Error on the R_c magnitude (S99) 81- 86 F6.3 mag Icmag I_c magnitude from KPNO/MOSA (S99) 88- 92 F5.3 mag e_Icmag Error on the I_c magnitude (S99) 94- 95 A2 --- --- [AP] (1) 97-115 A19 --- APname Object name (1)
Note (1): The numbering of the object conforms to the IAU convention. The prefix used is AP J for Alpha Per at the J2000 equinox: AP
Acknowledgements: Nicolas Lodieu, nl41(at)
(End) Nicolas Lodieu [Leicester Univ., UK], Patricia Vannier [CDS] 15-Mar-2005
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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