J/MNRAS/335/291 BVI photometry of NGC 2547 (Naylor+, 2002) ================================================================================ Optimal photometry for colour-magnitude diagrams and its application to NGC 2547 Naylor T., Totten E.J., Jeffries R.D., Pozzo M., Devey C.R., Thompson S.A. =2002MNRAS.335..291N (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Clusters, open ; Photometry, UBVRI Keywords: methods: data analysis - techniques: image processing - techniques: photometric - stars: formation - stars: pre-main sequence - open clusters and associations: individual : NGC 2547 Abstract: We have developed the techniques required to use Naylor's optimal photometry algorithm of to create colour-magnitude diagrams with well-defined completeness functions. To achieve this we first demonstrate that the optimal extraction is insensitive to uncertainties in the measured position of the star. We then show how to correct the optimally extracted fluxes such that they correspond to those measured in a large aperture, so aperture photometry of standard stars can be used to place the measurements on a standard system. The technique simultaneously removes the effects of a position-dependent point spread function. Finally, we develop a method called 'ghosting', which calculates the completeness corrections in the absence of an accurate description of the point spread function. We apply these techniques to the young cluster NGC 2547 (=C0809-491), and use an X-ray-selected sample to find an age of 20-35Myr and an intrinsic distance modulus of 8.00-8.15mag. We use these isochrones to select members from our photometric surveys. Our derived luminosity function shows a well-defined Wielen dip, making NGC 2547 the youngest cluster in which such a feature has been observed. Our derived mass function spans the range 0.1-6M_{sun}_ and is similar to that for the field and the older, more massive clusters M35 and the Pleiades, supporting the idea of a universal initial mass function. Description: The catalogues have been created using the optimal photometry algorithm described in Naylor (1998MNRAS.296..339N) and Naylor et al. (2002MNRAS.335..291N, this paper). Further information is also available from Tim Naylor's optimal photometry page ( http://www.astro.ex.ac.uk/people/timn/Photometry/description.html ). The catalogues are primarily in what is called cluster format, though there are occasional variations where they are needed. There is a deep survey (Table 3), a shallower, but wider area survey (Table 4), and the combination of these (Table 5). Extracted from the deep catalogue are tables of members of the cluster derived using either the D'Antona & Mazzitelli (1997MmSAI..68..807D) isochrones (Table 6). or the Siess (2000A&A...358..593S) isochrones (Table 7). These catalogues are the result of a collaboration between teams within the Exeter Astrophysics Group led by Tim Naylor, and the Keele Astrophysics Group led by Rob Jeffries. The contributors to the currently available catalogues are Tina Devey, Monica Pozzo (now at Imperial), Simon Thompson and Ed Totten. Objects: ----------------------------------------- RA (2000) DE Designation(s) ----------------------------------------- 08 10 25.7 -49 10 93 NGC 2547 ----------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 115 102 Combined catalogue entries for stars also in Claria (1982A&AS...47..323C) table3.dat 115 16649 Deep catalog table4.dat 115 25472 Wide catalog table5.dat 115 31880 Combined catalog table6.dat 43 184 D'Antona & Mazzitelli (1997MmSAI..68..807D) model table7.dat 43 201 Siess et al. (2000A&A...358..593S) model -------------------------------------------------------------------------------- Table 1: Log of observation ------------------------------------------------------------------ Field Field center Exposure (s) number RA (J2000) DE B V Ic ---------------------------------------------------------------------- 1 08 10 37.4 -49 17 40 3x200 3x100 3x80 2 08 09 33.6 -49 17 40 3x200 3x100 3x80 3 08 10 37.5 -49 07 10 3x200 3x100 3x80 4 08 09 33.6 -49 07 10 3x200 3x100 3x80 7 08 09 07.7 -49 23 30 30, 250 15, 100 15, 100 8 08 10 12.0 -49 23 30 30, 250 15, 100 15, 100 9 08 11 16.3 -49 23 30 30, 250 15, 100 15, 100 12 08 11 16.3 -49 13 00 30, 250 15, 100 15, 100 13 08 10 12.0 -49 13 00 2x30, 250 100 2x15, 100 14 08 09 07.7 -49 13 00 30, 250 15, 100 15, 100 17 08 09 07.7 -49 02 30 30, 250 15, 100 15, 100 18 08 10 12.0 -49 02 30 30, 250 15, 100 15, 100 19 08 11 16.3 -49 02 30 30, 250 15, 100 15, 100 ----------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat table3.dat table4.dat table5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- Claria ? Claria (1982A&AS...47..323C) number, NGC 2547 NNN in Simbad (only in table2.dat) 5- 6 I2 --- Field Field number 8- 11 I4 --- Star Star number in the field 14- 15 I2 h RAh Right ascension (J2000.0) 17- 18 I2 min RAm Right ascension (J2000.0) 20- 24 F5.2 s RAs [0/60] Right ascension (J2000.0) 26 A1 --- DE- Declination sign (J2000.0) 27- 28 I2 deg DEd Declination (J2000.0) 30- 31 I2 arcmin DEm Declination (J2000.0) 33- 37 F5.2 arcsec DEs [0/60] Declination (J2000.0) 40- 47 F8.3 pix Xpos X position in the CCD image 50- 57 F8.3 pix Ypox Y position in the CCD image 59- 65 F7.3 mag Vmag V magnitude 67- 73 F7.3 mag e_Vmag rms uncertainty on Vmag 75- 76 I2 --- f_Vmag Flag on Vmag (1) 78- 84 F7.3 mag B-V B-V colour index 86- 92 F7.3 mag e_B-V rms uncertainty on B-V 94- 95 I2 --- f_B-V Flag on B-V colour (1) 97-104 F8.3 mag V-Ic V-Ic colour index 106-112 F7.3 mag e_V-Ic rms uncertainty on V-Ic 114-115 I2 --- f_V-Ic Flag on V-Ic colour (1) -------------------------------------------------------------------------------- Note (1): Flags: The flags are two digit numbers. Each digit is the flag for one of the two filters which went to making up the colour. For simple magnitudes, one flag is for the filter for that magnitude, the other flag is for the other filter which was used for the colour term. The first flag is always for the bluer of the two filters. For example, a V magnitude whose colour term was derived from B-V, might have a flag of 13. This would mean that the instrumental B measurement had been flagged 1 and instrumental V as 3. The flags are divided into strong and weak. A strong flag will always be written, overwriting any other flags, whilst a weak flag will only be written if the measurement is unflagged so far. Thus the order the flags are applied is important. Most flags are strong, a weak flag is only used if there might be reason to trust the resulting photometry. The ill-determined sky criterion is very cautious, so if inspection of the image suggests the the sky is not strongly structured, such data can be useful. Similarly patching bad pixels can work very well, at which point images on bad pixels may be worthwhile. The list of flags, in the order they are applied, is as follows. ----------------------------------------------------------------------- Number Name Algorithm Type ----------------------------------------------------------------------- 0 No problem 1 Non-stellar Star shape estimator Strong 2 Too close to edge Position fitting Strong 3 Sky fit failed Sky determination Strong 5 Ill-determined sky Sky determination Weak 4 Saturated Flux measurement Strong 2 Too close to edge Flux measurement Strong 8 Bad pixel Bad pixel flagging Strong 7 No input data Data input Strong 9 Negative counts Data input Weak 6 Variable Combining images Strong ----------------------------------------------------------------------- If a star is flagged as having negative counts (9), the error column is set to the modulus of the flux, converted into magnitudes. The magnitude is replaced with the flux error bar converted into magnitudes. Thus magnitudes for objects flagged 9 should be treated as bright limits. It also means that colours which are quoted for these objects are limits. For example a flag of 90 in the BV colour, means that the B magnitude is a lower limit, so B-V is a lower limit. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table6.dat table7.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 2 I2 --- Field Field number 4- 7 I4 --- Star Star number in the field 10- 11 I2 h RAh Right ascension (J2000.0) 13- 14 I2 min RAm Right ascension (J2000.0) 16- 21 F6.3 s RAs Right ascension (J2000.0) 23 A1 --- DE- Declination sign (J2000.0) 24- 25 I2 deg DEd Declination (J2000.0) 27- 28 I2 arcmin DEm Declination (J2000.0) 30- 34 F5.2 arcsec DEs Declination (J2000.0) 37 I1 --- fmemb1 [0/1] Membership flag in V vs B-V (1) 39 I1 --- fmemb2 [0/1] Membership flag in V vs V-I (1) 41 I1 --- fmemb3 [0/1] Membership flag in B-V vs V-I (1) 43 I1 --- fmemb4 [0/1] Membership flag for binary (2) -------------------------------------------------------------------------------- Note (1): Membership flag: 1 if the star is a member in the appropriate colour combination, 0 if that combination is unavailable (which includes the signal-to-noise being too low) Note (2): This flag is a shows whether the colour 1 (V) vs colour 2 (B-V) plot indicates the star is binary (i.e. it lies above the sequence - see paper for details), 0=binary, 1=single. -------------------------------------------------------------------------------- Acknowledgements: Tim Naylor ================================================================================ (End) Patricia Bauer [CDS] 06-Dec-2002