SDSS griz photometry
(first experiences at Baja Observatory)
T. Hegedüs – A. Szing – J. Vinkó*
Baja Astronomical Observatory, * Szeged University
KOLOS 2013
First Standardized photometric system: Johnson’s UBV (1950…)
Harold Lester Johnson (April 17, 1921 – April 2, 1980)
UBV system: based on photomultipliers (basically blue-sensitive)
Sloan Digital Sky Survey (2000-…)
Apache Point Observatory (New Mexico, US)
D=2,5 m RC telescope – at 2788 m altitude
65% clear sky
3 deg. large field of view
30 x 4 Mpixels CCD (cooled to -80C LN)
58x58 mm
Made by Omega Optical
Filter
u'
g'
r'
i'
z'
g  r '
r  i '
Supported by Masaryk Univ.
r  z '
Brno (Cz) & Szeged University (Hu)
λc (Å)
3543
4770
6231
7625
9134
FWHM (Å)
570
1370
1370
1530
950
= a1  g  r obs + b1
= a2  r  i obs + b2
= a3  r  z obs + b3
r' robs = a4  g  i obs + b4
Average scatter at Baja (July-August 2013)
SN 2012ht
SN 2013dy
SN 2013df
SN 2013ej
New griz photometry project: monitoring blazars in Kepler field
2541 BZBJ1838+4802
2606 BZQJ1949+5041
2618 BZBJ2001+4352
2635 BZBJ2012+4628
18 38 49.0
19 49 43.3
20 01 12.8
20 12 05.5
+48 02 34.0
+50 41 31.9
+43 52 51.9
+46 28 54.9
0
1.929
0
0
16.2 BL Lac
15.7 QSO RLoud flat radio sp.
15
BL Lac
16.8 BL Lac
Problem: there are no ‘griz’ standards near this area!
Solution ???
One possible solution: usage of previous UBVRI standards
and try to transform
For Kepler-field blazars we selected NGC7790 open cluster’s standards.
At the SDSS web site:
http://www.sdss.org/dr7/algorithms/sdssUBVRITransform.html#Jordi2006
One can find the possible linear formulae (Jordi et al., 2006)
UBVRcIc -> ugriz
================
Transformation
u-g =
(0.750 ± 0.050)*(U-B) + (0.770 ± 0.070)*(B-V) + (0.720 ± 0.040)
* g-V =
(0.630 ± 0.002)*(B-V) - (0.124 ± 0.002)
g-B =
(-0.370 ± 0.002)*(B-V) - (0.124 ± 0.002)
* g-r =
(1.646 ± 0.008)*(V-R) - (0.139 ± 0.004)
g-i =
(1.481 ± 0.004)*(V-I) - (0.536 ± 0.004) if V-I <= 1.8
g-i =
(0.83 ± 0.01)*(V-I)
+ (0.60 ± 0.03) if V-I > 1.8
* r-i =
(1.007 ± 0.005)*(R-I) - (0.236 ± 0.003)
* r-z =
(1.584 ± 0.008)*(R-I) - (0.386 ± 0.005)
r-R =
(0.267 ± 0.005)*(V-R) + (0.088 ± 0.003) if V-R <= 0.93
r-R =
(0.77 ± 0.04)*(V-R)
i-I =
- (0.37 ± 0.04) if V-R > 0.93
(0.247 ± 0.003)*(R-I) + (0.329 ± 0.002)
(Jordi et al. (2006)
New experiment: another SDSS system on 50 cm RC telescope
Just for fun… (2013. 11. 15. BART-1, Baja Observatory, Hu
Thank you for your attention!
Comet Lovejoy