Stellar properties of objects in the SXDS ================================================================================ ADC_Keywords: Combined data ; Galactic pole, north ; Stars, faint Keywords: stars: statistics -- methods: data analysis Abstract: We investigate the properties of objects in the Subaru/XMM-Newton Deep Survey (SXDS), using public catalogs constructed from images in several optical passbands. Using a small subset of objects most likely to be stars, we construct a stellar locus in three-dimensional color space. We then compare the position of all objects relative to this locus to create larger samples of stars in the SXDS with rough spectral types. Description: Using photometry and other parameters provided in the SXDS catalogs (beta version, http://soaps.naoj.org/sxds/), we have constructed a stellar locus in three-dimensional space, following closely the procedure described in Richmond (2005). We assign each object two scores: a morphological one, based on its shape, and a color one, based on its proximity to the stellar locus in color space. We have calibrated how position along the stellar locus corresponds to spectral type, so that we can assign a rough spectral type to every object (which will be meaningful only for objects actually near the stellar locus). We include information for all objects in the SXDS i'-based catalogs, even those which are obviously not stars (because they are clearly extended and/or far from the stellar locus), so that the user can choose the exact cutoff between stars and galaxies, or create a catalog of non-stellar objects in the SXDS. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file sxds_locus_class.dat 210 780826 Measured and derived properties of all qualifying objects in the SXDS i'-based catalogs -------------------------------------------------------------------------------- Byte-by-byte Description of file: sxds_locus_class.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 6 I6 --- Index Sequential index number 8- 18 F11.5 deg RA Right ascension (J2000.0) 20- 30 F11.5 deg Dec Declination (J2000.0) 33- 40 F8.4 mag Bmag Magnitude in Johnson B passband 42- 49 F8.4 mag Vmag Magnitude in Johnson V passband 51- 58 F8.4 mag Rcmag Magnitude in Cousins Rc passband 60- 67 F8.4 mag ipmag Magnitude in Suprime-Cam i-prime passband 69- 76 F8.4 mag zpmag Magnitude in Suprime-Cam z-prime passband 78- 81 F4.2 --- B_cls "class_star" value in B image (1) 83- 86 F4.2 --- V_cls "class_star" value in V image (1) 88- 91 F4.2 --- Rc_cls "class_star" value in Rc image (1) 93- 96 F4.2 --- ip_cls "class_star" value in i-prime image (1) 98-101 F4.2 --- zp_cls "class_star" value in z-prime image (1) 103-108 F6.3 mag B_delta difference of aperture magnitudes in B (2) 110-115 F6.3 mag V_delta difference of aperture magnitudes in V (2) 117-122 F6.3 mag Rc_delta difference of aperture magnitudes in Rc (2) 124-129 F6.3 mag ip_delta difference of aperture magnitudes in i-prime (2) 131-136 F6.3 mag zp_delta difference of aperture magnitudes in z-prime (2) 138-139 I2 --- m_score overall morphological score (3) 141-146 F6.3 mag xpos (B-V) color = x-position in color-color space 148-153 F6.3 mag ypos (V-R) color = y-position in color-color space 155-160 F6.3 mag zpos (R-i) color = z-position in color-color space 164-169 F6.2 mag milestone distance from end of stellar locus (4) 172-176 F5.2 --- c_score color score (5) 179-186 A1 --- spectype rough spectral type, based on milestone 189-191 I3 --- locus index of locus node closest to object 194-200 F7.3 mag ldist distance from object to stellar locus, measured along major axis of locus (6) 202-208 F7.3 mag mdist distance from object to stellar locus, measured along minor axis of locus -------------------------------------------------------------------------------- Note (1): The "class_star" value is a measure of how star-like an object appears, based on SExtractor output. We copy this value directly from the beta versions of the SXDS public catalogs at http://soaps.naoj.org/sxds/. The value ranges from 0.0 (very extended) to 1.0 (very star-like). Note (2): The "delta" value is the difference between the magnitude measured in an aperture of radius 2 arcseconds and the magnitude measured in an aperture of radius 3 arcseconds. We find that values in the range 0.08 < delta < 0.23 are roughly consistent with point-like objects. Note (3): For each of the 5 passbands, we make 2 tests based on the shape of an object: we ask if its "class_star" value is greater than some value (typically 0.90, small variations from field to field), and if its "delta" value is in the range appropriate for stars (typically 0.10 < delta < 0.20, with small variations from field to field). Each test passed counts as 1. This score is the sum of all tests: it ranges from 0 (not star-like) to 10 (very star-like). Note (4): We first find the closest approach of the stellar locus to the colors of each object, then measure the distance along the locus to that closest approach. Distance of zero corresponds approximately to spectral class B4. Note (5): A measure of the degree to which the colors of this object (including their uncertainties) fall within the stellar locus at the point of closest approach. Values range from 0.0 (color is completely outside the stellar locus) to 1.0 (color is completely within the locus). Note (6): The position of a star within the locus may in some regions correlate with its metallicity. At the red end of the locus, positive values of "ldist" are more likely for metal-rich stars, while negative values of "ldist" are more likely for metal-poor stars. -------------------------------------------------------------------------------- Acknowledgements: References: Richmond, M. W., 2005PASJ...57..969R Properties of Stars in the Subaru Deep Field ================================================================================ (End) Michael Richmond [RIT, USA] 08-Mar-2006