Thursday, November 8, 2012

CFHT quick-look

[Technical post about ongoing project.]

To examine colours of one quasar in CFHT imaging:

Locate g, r, i images of quasar. [in this example, they are 1571 + 386p, 397p, 408p]

Create coordinates file of comparison stars on same chip which are not saturated in any filter and thus can be used to calculate the aperture correction in all filters:

photcal> head j224733.coo.1
1066 1271
1204 3015
208 2956
686 1348
521 1321

Create coordinates file of quasar:

photcal> head j224733.coo.2
752 1385

In IRAF, load noao.digiphot, type "datapars", and make sure these parameters are set:

(ccdread=              RDNOISE) CCD readout noise image header keyword
(gain   =                     ) CCD gain image header keyword
(readnoi=                   0.) CCD readout noise in electrons
(epadu  =                   1.) Gain in electrons per count
(exposur=              EXPTIME) Exposure time image header keyword
(airmass=              AIRMASS) Airmass image header keyword
(filter =               FILTER) Filter image header keyword

In photpars, I set:
apertur= 5,7.5,10,12.5,15,17.5,20,22.5,25,27.5,30,35,40,45,50
which I recommend doing, to help identify any outlier stars in the aperture correction phase.

Photometer comparison stars & quasars separately:
(I couldn't get e.g. "phot 1571386p.fits[ccd03]" to work, so I first copied the extensions to individual images, but I see now that I should have just done "phot 1571386p.fits[3]".) 

imcopy 1571386p.fits[ccd03] 1571386p03.fits
phot 1571386p03.fits coo=j224733.coo.1 interac-
phot 1571386p03.fits coo=j224733.coo.2 interac-

imcopy 1571397p.fits[ccd03] 1571397p03.fits
phot 1571397p03.fits coo=j224733.coo.1 interac-
phot 1571397p03.fits coo=j224733.coo.2 interac-

imcopy 1571408p.fits[ccd03] 1571408p03.fits
phot 1571408p03.fits coo=j224733.coo.1 interac-
phot 1571408p03.fits coo=j224733.coo.2 interac-

Use output to calculate aperture correction between aperture 1 (5 pixels) and aperture 9 (25 pixels) using the "mkapfile" task in the "photcal" package in noao.digiphot:

mkapf 1571386p03.fits.mag.1  9 1571386p03.apcor.1 small=1 large=9
mkapf 1571397p03.fits.mag.1  9 1571397p03.apcor.1 small=1 large=9 nparams=2
mkapf 1571408p03.fits.mag.1  9 1571408p03.apcor.1 small=1 large=9

[r-band apcor wouldn't converge unless number of free parameters was reduced]

Extract quasar magnitude and apply aperture correction in each filter (all IRAF commands):
txdump 1571386p03.fits.mag.2 mag yes | scan (x)
txdump 1571386p03.fits.mag.2 merr yes | scan (y)
fields 1571386p03.apcor.1 3 | sort num+ rev+ | scan (z)
fields 1571386p03.apcor.1 2 | sort num+ rev+ | scan (z)
printf("%7.3f %6.3f %8.3f\n",x,y,z, >> "1571386p03.mea")
txdump 1571397p03.fits.mag.2 mag yes | scan (x)
txdump 1571397p03.fits.mag.2 merr yes | scan (y)
fields 1571397p03.apcor.1 3 | sort num+ rev+ | scan (z)
fields 1571397p03.apcor.1 2 | sort num+ rev+ | scan (z)
printf("%7.3f %6.3f %8.3f\n",x,y,z, >> "1571397p03.mea")
txdump 1571408p03.fits.mag.2 mag yes | scan (x)
txdump 1571408p03.fits.mag.2 merr yes | scan (y)
fields 1571408p03.apcor.1 3 | sort num+ rev+ | scan (z)
fields 1571408p03.apcor.1 2 | sort num+ rev+ | scan (z)
printf("%7.3f %6.3f %8.3f\n",x,y,z, >> "1571408p03.mea")

head 1571*p03.mea
===> 1571386p03.mea <=== -6.1195  0.023   -0.307 g
===> 1571397p03.mea <=== -6.374  0.014   -0.178 r
===> 1571408p03.mea <=== -6.437  0.014   -0.214 i

Table of values useful for calculating calibrated magnitudes:

filter              g       r       i
exptime 52.071  85.049  144.052
X_?        1.295   1.225   1.153
?_c       26.485  26.020  25.840
?_c_err 0.0098  0.0076  0.0070
?_X        0.148   0.0     0.0830
?_K       -0.15   -0.10   -0.040
g,r,i     -6.1195 -6.374  -6.437

Calculate calibrated magnitudes; R then G then I:

#R = r + r_c + r_K*(X_r-1)
= -6.374 + 26.020 -0.10*0.225   # 19.624
= sqrt(0.014**2.+0.0076**2.)    #  0.016
=(-6.1195 + 26.485 + -0.15*0.295 - 0.148*19.624)/(1-0.148) # 20.442
= sqrt(0.023**2.+0.0098**2.)    #                                             0.025
=(-6.437+25.840+ -0.04*0.153 +0.083*19.624)/(1+0.083) #  19.414
= sqrt(0.014**2.+0.0070**2.)    #                                          0.016

G         R         I
20.442 19.624 19.414
+-0.025  0.016  0.016

=20.442-19.624; = sqrt(0.025**2.+0.016**2.) #G-R & err
=19.624-19.414; =sqrt(0.016**2.+0.016**2.) #R-I & err

G-R = 0.82 +- 0.03
R-I = 0.21 +- 0.02

These values match those observed in Stripe 82 for this quasar.  No evidence that the blue shape of the BOSS spectra in between S82 and CFHT epochs is real.

(A check of one comparison star confirms that the CFHT magnitude scale is close enough to the SDSS magnitude scale that the above conclusion will not be invalidated by systematic errors.)

Friday, October 5, 2012


Check out an interview with me on the Star Spot Podcast!  (I apologize in advance for my audio fading in and out.  Maybe I should just speak loudly and excitedly all the time!  Whatever the solution, clearly I need more practice keeping my voice evenly modulated in interviews.)

Wednesday, October 3, 2012

Both Sides Now

PSU grad student Nur Filiz Ak led a project that watched clouds (of a sort) clear out from in between us and some distant black holes... cool to be part of that.

And we just submitted a proposal to look at clouds that have appeared in quasar spectra.  We think the clouds are moving into and out of our line of sight.  If approved, our recent proposal means we'll have looked at the leading and trailing sides of clouds, hence the title of this post...

Tuesday, October 2, 2012

Length of the Seasons, 2011-2012

Fun fact: because Earth's perihelion currently occurs in early January, it is moving faster in its orbit during northern hemisphere fall and winter.  So the northern hemisphere currently gets a week more spring+summer than fall+winter.


Behold the math:

In 2011-2012, length of the northern hemisphere seasons in minutes:

Dec 22 05 30 to Dec 31 24 00 plus
Jan 01 00 00 to Mar 20 05 14: = (9*24+18.5)*60 + ((31+29+19)*24+(5+14/60.))*60

Mar 20 05 14 to Jun 20 23 09: = ((11+30+31+19)*24+(18+46/60.+23+9/60.))*60

Jun 20 23 09 to Sep 22 14 49: = ((10+31+31+21)*24+(0+51/60.+14+49/60.))*60

Sep 22 14 49 to Dec 21 11 12: = ((8+31+30+20)*24+(9+11/60.+11+12/60.))*60

ecl> =128144+129383-134860-133555
ecl> =10888/(24*60.)

sanity check:

Astronomy Activities Manual

Last month saw the publication of my "Astronomy Activities Manual" from Kendall Hunt. If you're looking for in-class activities and a few lab exercises and assignments for students in your undergrad intro astro class, Kendall Hunt has published a wide of activities by numerous authors over the years. You can pick and choose the ones you like and put them together into a custom workbook (and the authors get royalties). I've taken existing activities that I think will work well in my class and added a dozen or so of my own, mostly for the extragalactic half of the course. If you're interested, check out the table of contents below and contact Richard Ludlow at Kendall Hunt (rludlow At to get a sample copy.  (PS - it's not a typo; there is no Lab IV in the book.)

Monday, September 24, 2012

Proposal Season

Kept waiting for this blog to resurrect itself, but doesn't seem to have a self-writing option yet. To catch up: Over the summer I submitted one paper and my senior grad student & I submitted another. Plus my junior grad student & I started receiving the CFHT data for which we proposed in the spring. And a book of university-level astronomy in-class activities (half mine, half others) has been published. Right now I am working on telescope proposals, but should blog more often once they are in.

Thursday, April 19, 2012

Asteroid Pathall

A bunch of asteroids were discovered in the Sloan Digital Sky Survey, in which I was involved. So the asteroid scientists in the SDSS decided to name an asteroid after each of the several hundred scientists involved in the SDSS. It took a couple years, and I didn't want to say anything until it came through, but it finally did, and now I have an asteroid named after me. You can see asteroid Pathall here. If you zoom in, you see a green, a red, and a blue image from upper left to lower right. Photos in those colors were taken about a minute apart, and because the asteroid is moving the images are offset from each other. This asteroid hangs out beyond Mars, and is probably about 10 km on a side. It has an orbit with an eccentricity of 0.1491 (on a scale of 0 to 1), which is slightly disappointing; a more eccentric object would have been more appropriate to name after me, I think...

Wednesday, February 1, 2012


Have been writing a lot of in-class activities for my intro astro course, testing them out in preparation for inclusion in an in-class activity workbook to be published next year through Kendall-Hunt.  Was driven to change from the activity book I've used for the past 3 years because a significant # of students would bring the workbook to class but not fill it in, because they wanted to sell it back at the end of the year!  So I told them I'm going to change workbooks next year, rendering sell-back difficult if not impossible.  Kendall-Hunt has a lot of activity books from which to pick and choose activities to include in your own book, in addition to providing ones of your own (I find I have to provide the bulk of the stellar and extragalactic activities, as those are rather rare).  Workbook will also include labs, like the new one on transiting extrasolar planets I just wrote.

Also am teaching an upper-division/graduate course on stars & nebulae.

Also am on a theory-faculty job search committee.  146 applicants!  Ha ha I remember what having time for research used to be like.

Still, with last week's arrival of my postdoc Paola Rodriguez Hidalgo, it's time to bring research back into the mix.  For example, I have an idea for using variability in BAL troughs to constrain the small-scale structure of quasar accretion disks...