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Changes between Initial Version and Version 1 of FaintBias


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Timestamp:
Jan 26, 2012, 2:46:32 PM (15 years ago)
Author:
schlafly
Comment:

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  • FaintBias

    v1 v1  
     1= Faint-end bias investigation (Eddie Schlafly) =
     2
     3I've been investigating correcting the faint-end bias in PS1 stellar photometry empirically over the past several days.  Doug Finkbeiner has found that the bias can be seen comparing PS images to PS images with different PSF FWHM, and that this bias can be well modeled as a constant offset in flux (e.g., the following plot).
     4
     5[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbias/example1.png)]]
     6
     7Motivated by this, I have fit a function of this form to every PS image overlapping the SDSS, transforming the SDSS magnitudes onto the PS system following JT's color transformations.  This produces a list of flux offsets for every PS1 image.  I want to use this information to remove the faint-end bias in all of the PS1 images.
     8
     9== Trend in bias with FWHM ==
     10
     11There is a clear relation in the flux offset as a function of PSF FWHM, consistent with what Doug found.  The relation is different for exposures in different filters and with different exposure times.  Unfortunately, I haven't been able to figure out what controls the differences in these relations.  Accordingly, I have just fit a quadratic for the flux offset as a function of PSF FWHM for every exposure time and filter combination.  Additionally, I found that the residuals in this relation changed around MJD 55660, and so I fit separation relations before and after that date.  The relevant plots describing these fits follow.  The title gives the filter, exposure time, and MJD range corresponding to each plot.  The 30s y band plot shows what look like two loci, but I haven't been able to figure out what controls the two loci; there is no clear split in MJD or sky background or any other parameter I have looked at.
     12
     13[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113(55660-inf).png)]]
     14[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113(-inf-55660).png)]]
     15[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g240(-inf-inf).png)]]
     16[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g43(55660-inf).png)]]
     17[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g43(-inf-55660).png)]]
     18[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g52(-inf-55660).png)]]
     19[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113(55660-inf).png)]]
     20[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113(-inf-55660).png)]]
     21[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r240(-inf-inf).png)]]
     22[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r36(-inf-55660).png)]]
     23[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r40(55660-inf).png)]]
     24[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r40(-inf-55660).png)]]
     25[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r60(-inf-inf).png)]]
     26[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240(55660-inf).png)]]
     27[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240(-inf-55660).png)]]
     28[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i32(-inf-55660).png)]]
     29[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i45(55660-inf).png)]]
     30[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i45(-inf-55660).png)]]
     31[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z20(-inf-inf).png)]]
     32[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240(55660-inf).png)]]
     33[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240(-inf-55660).png)]]
     34[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30(55660-inf).png)]]
     35[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30(-inf-55660).png)]]
     36[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240(55660-inf).png)]]
     37[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240(-inf-55660).png)]]
     38[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y30(55660-inf).png)]]
     39[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y30(-inf-55660).png)]]
     40
     41== Test of corrected data ==
     42
     43I have then tested applying these relations to images drawn at random from the survey.  What follows are a large number of examples of the original data, and then the data corrected according to the relations above.  I think the moral is that the correction does substantially more good than harm.  Nevertheless, there are clear examples where the correction fails badly.
     44
     45g 113s
     46
     47[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113o5251g0315o.140316.cm.50480.png)]]
     48[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113o5479g0079o.237418.cm.128173.png)]]
     49[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113o5584g0566o.285261.cm.163780.png)]]
     50[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113o5587g0557o.287505.cm.165634.png)]]
     51[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113o5614g0254o.304643.cm.176183.png)]]
     52[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113o5665g0270o.323460.cm.193488.png)]]
     53[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113o5767g0500o.368085.cm.239892.png)]]
     54[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113o5776g0416o.372285.cm.243824.png)]]
     55[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g113o5812g0351o.389175.cm.262313.png)]]
     56
     57g 240s
     58
     59[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g240o5014g0017o.84016.cm.110311.png)]]
     60[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g240o5828g0212o.398809.cm.274325.png)]]
     61[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g240o5828g0222o.398819.cm.274349.png)]]
     62
     63g 43s
     64
     65[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g43o5389g0402o.191736.cm.96638.png)]]
     66[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g43o5446g0275o.221000.cm.115108.png)]]
     67[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g43o5480g0557o.238390.cm.128857.png)]]
     68[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g43o5563g0298o.271504.cm.156357.png)]]
     69[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g43o5676g0187o.329346.cm.198005.png)]]
     70[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g43o5745g0346o.356720.cm.229845.png)]]
     71[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g43o5797g0141o.381642.cm.252912.png)]]
     72
     73g 52s
     74
     75[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g52o5242g0461o.135993.cm.44982.png)]]
     76[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/g52o5276g0177o.150138.cm.61403.png)]]
     77
     78r 113s
     79
     80[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113o5413g0123o.202995.cm.103038.png)]]
     81[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113o5440g0434o.217489.cm.112486.png)]]
     82[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113o5590g0591o.289723.cm.167238.png)]]
     83[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113o5593g0123o.291166.cm.168437.png)]]
     84[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113o5629g0074o.306275.cm.181382.png)]]
     85[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113o5761g0095o.364733.cm.236426.png)]]
     86[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113o5764g0097o.366395.cm.238063.png)]]
     87[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113o5773g0523o.370606.cm.242041.png)]]
     88[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r113o5821g0277o.393199.cm.269672.png)]]
     89
     90r 240s
     91
     92[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r240o5014g0021o.84020.cm.110313.png)]]
     93[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r240o5828g0233o.398830.cm.274385.png)]]
     94[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r240o5828g0234o.398831.cm.274386.png)]]
     95[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r240o5828g0353o.398950.cm.274507.png)]]
     96[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r240o5828g0354o.398951.cm.274508.png)]]
     97
     98r 36s
     99
     100[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r36o5247g0044o.137655.cm.48612.png)]]
     101[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r36o5248g0373o.138455.cm.49231.png)]]
     102[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r36o5298g0383o.156806.cm.73453.png)]]
     103
     104r 40s
     105
     106[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r40o5502g0168o.249478.cm.135885.png)]]
     107[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r40o5767g0177o.367762.cm.239864.png)]]
     108[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r40o5860g0408o.414635.cm.308637.png)]]
     109
     110r 60s
     111
     112[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r60o5163g0176o.105438.cm.88654.png)]]
     113[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r60o5163g0184o.105446.cm.88659.png)]]
     114[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/r60o5163g0186o.105448.cm.88660.png)]]
     115
     116i 240s
     117
     118[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240o5339g0049o.171150.cm.80799.png)]]
     119[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240o5447g0277o.221521.cm.115317.png)]]
     120[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240o5504g0259o.251004.cm.137108.png)]]
     121[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240o5576g0471o.280585.cm.160011.png)]]
     122[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240o5576g0644o.280758.cm.160127.png)]]
     123[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240o5738g0094o.353113.cm.225669.png)]]
     124[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240o5777g0055o.372427.cm.243999.png)]]
     125[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240o5804g0087o.384586.cm.256174.png)]]
     126[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i240o5804g0518o.385017.cm.256529.png)]]
     127
     128i 32s
     129
     130[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i32o5248g0138o.138220.cm.49100.png)]]
     131[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i32o5250g0271o.139657.cm.50250.png)]]
     132[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i32o5258g0196o.144831.cm.55640.png)]]
     133[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i32o5282g0197o.152058.cm.63203.png)]]
     134
     135i 45s
     136
     137[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i45o5351g0157o.176929.cm.84410.png)]]
     138[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i45o5577g0393o.281273.cm.160392.png)]]
     139[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i45o5577g0468o.281348.cm.160483.png)]]
     140[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i45o5722g0116o.345929.cm.218855.png)]]
     141[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i45o5724g0179o.347078.cm.219719.png)]]
     142[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/i45o5791g0240o.378336.cm.249626.png)]]
     143
     144z 20s (weird camera testing images, but in my copy of the database anyway)
     145
     146[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z20c5799g0011o.382220.cm.253876.png)]]
     147[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z20c5799g0019o.382228.cm.253891.png)]]
     148[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z20c5799g0021o.382230.cm.253894.png)]]
     149[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z20c5799g0022o.382231.cm.253896.png)]]
     150[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z20c5799g0024o.382233.cm.253898.png)]]
     151
     152z 240s
     153
     154[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240o5241g0210o.135249.cm.44215.png)]]
     155[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240o5250g0501o.139891.cm.50064.png)]]
     156[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240o5304g0069o.158595.cm.74014.png)]]
     157[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240o5322g0296o.161478.cm.76125.png)]]
     158[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240o5481g0035o.238522.cm.129026.png)]]
     159[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240o5712g0054o.342671.cm.215619.png)]]
     160[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240o5775g0529o.371779.cm.243286.png)]]
     161[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240o5799g0368o.382561.cm.254137.png)]]
     162[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z240o5854g0333o.410066.cm.305806.png)]]
     163
     164z 30s
     165
     166[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30o5255g0359o.143120.cm.53426.png)]]
     167[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30o5255g0708o.143449.cm.53703.png)]]
     168[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30o5547g0060o.265953.cm.151473.png)]]
     169[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30o5636g0193o.311238.cm.184607.png)]]
     170[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30o5694g0088o.335318.cm.209156.png)]]
     171[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30o5814g0164o.390120.cm.263874.png)]]
     172[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30o5814g0462o.390418.cm.264048.png)]]
     173[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/z30o5863g0046o.415289.cm.310066.png)]]
     174
     175y 240s
     176
     177[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5017g0027o.84780.cm.110333.png)]]
     178[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5257g0465o.144514.cm.55228.png)]]
     179[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5403g0196o.197245.cm.99477.png)]]
     180[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5430g0291o.211036.cm.108534.png)]]
     181[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5434g0124o.213464.cm.110158.png)]]
     182[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5669g0231o.325836.cm.195069.png)]]
     183[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5755g0508o.361274.cm.233356.png)]]
     184[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5800g0085o.382688.cm.254424.png)]]
     185[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5800g0087o.382690.cm.254435.png)]]
     186[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y240o5837g0053o.402142.cm.283056.png)]]
     187
     188y 30s
     189
     190[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y30o5267g0535o.147178.cm.57349.png)]]
     191[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y30o5557g0130o.268377.cm.153126.png)]]
     192[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y30o5646g0111o.316495.cm.187830.png)]]
     193[[Image(http://faun.rc.fas.harvard.edu/eschlafly/faintbiasfigs/y30o5701g0033o.338773.cm.212208.png)]]