Tuesday, November 19, 2013

Gas Falling(?) Toward Black Holes

I've had a bit of publicity lately with a press release about some unusual quasars I've found.

READ the York press release!

OR READ INSTEAD the Penn State press release!

MARVEL at the Colour Illustrations!  (Click on an illustration to read its caption.)

JOIN ME in my bafflement at this 'BLACK HOLE-QUASAR'!

TREMBLE at these Things Which Should Not Be!

DISCOVER the odd (yet oddly understandable) headlines other writers come up with!

RETURN to the previous blog post to view animated gifs of these oddities!

Science marches on!

Friday, November 15, 2013

Animated accretion disk outflows

Choose any arrowhead below and watch its tip to see the rotation and outflow from these illustrations of accretion disks and their winds.  It ain't CGI, but it's still useful.  Refresh to restart.

An earlier effort (again, refresh to restart):

Thursday, November 7, 2013

Looking for the counterpart of the naked-eye optical transient OT120926

Just as we resubmitted our paper on "OT120926", a transient astronomical object briefly visible to the naked eye, DASCH released more data.  DASCH is the Digital Access to a Sky Century at Harvard: over 100 years of photographic plate images of the sky digitized and put online.  The location of OT120926 is in the new data release, but even DASCH does not solve the mystery of what object on the sky was responsible for this bright, transient flare.

Neither of the two bright stars near the position of OT 120926 show any sign of flares in over 1000 images.  The fainter nearby star SDSS J1436+1553 shows no sign of flaring in 15 images.

The presumed M dwarf star LP 440-48 has a possible detection in 1905.252749 (plate ac06251), shown in the first thumbnail below.  [All thumbnails show star BD+16 2671 at center and star TYC 1477-341-1 at top, just left of center.]

First thumbnail
First thumbnail
Second thumbnail
Second thumbnail

Third thumbnail
Third thumbnail

The first thumbnail shows an object in the left half of the image which could be LP 440-48 in a flare to magnitude ~11.6.  However, the second thumbnail is the very next image of the field in the DASCH database (1905.263690, plate ac06267), and it shows a possible object between BD +16 2671 and TYC 1477-341-1.  And the third thumbnail is the next image after that in DASCH (1905.280362, plate am03455), showing a possible object to the right of BD +16 2671.

The presence of three one-off "objects" in a rough arc on three images taken in sequence four and then six days apart makes the identification of LP 440-48 in a flare on the first image uncertain.  On the other hand, DASCH images taken shortly before and after the sequence above show no further evidence for a single moving object (like an asteroid) which might explain the observations.

Detailed inspection of the images and scanned plates might help determine whether the "objects" in question are likely to be real astronomical sources or just plate flaws or other artifacts, but such a task is beyond the scope of this investigation.  A more straightforward way forward would be to obtain a spectrum of LP 440-48 and to look for any signs of stellar activity in it; such a spectrum has been obtained by Mansi Kasliwal (Carnegie).

Still, it's cool to be using photographs of the sky taken over 100 years ago for science!

Wednesday, July 24, 2013


Today I finally got tired of there not being an IRAF task for smoothing a spectrum in text format, so I wrote one.  Also made good progress on getting a paper ready to submit for publication.

Saturday, July 20, 2013


This blog has annoyingly failed to become self-aware and update itself, so...

Two undergraduates working with me on research this summer.
I'll post their starter projects on the Moon and ? Boo soon.
They've moved on to studying quasar accretion disc temperature profiles and quasar spectra, so those topics will get posts soon too.

Work on quasar absorption lines continues apace.  My grad student Jesse Rogerson has been working on our Gemini data from the past semester.  When SDSS DR10 drops, we'll be working to identify new targets for Gemini right away.
Next week I'll start juggling that work with a return to modelling emission lines from disc winds, which my grad student Laura Chajet is also working on in preparation for a conference later this summer.

Tuesday, April 9, 2013

? Boo

In a term project picked up from my York colleague Paul Delaney, undergraduate non-science majors in my intro astro class photograph a constellation.  While doing so last fall, one student may have discovered a previously unknown flare star in Bootes, flaring to 5th magnitude next to omicron Boo and pi Boo.  We have dubbed this object "? Boo".

Details are available at http://www.aavso.org/possible-flare-star-bootis ...including a link to astrometry.net where I was able to get an astrometric calibration of the field:

Being busy with other projects, I'm restraining myself from trawling through online archival databases to look for evidence of variability in either of the two candidate stars that might have hosted this flare.

Another thing to restrain myself from (for a while) is to take the 1/8th second exposure handheld image, in which the stars have the shape of a seeing disk trailed in a complicated pattern due to jitter, and see if I can get better astrometry from it than from the 2 second exposure, in which the stars have the shape of a seeing disk trailed over and over itself until it's just a blurry blob.  By isolating the brightest part of each star in the 1/8th second image, it may be possible to measure the astrometric position of ? Boo to the limit allowed by seeing or pixel size rather than by handheld blurring.  Speckle interferometry on the cheap!  And if you're reading this and are intrigued by this idea, go ahead and try it!

Thursday, March 14, 2013

Marching On

Too long since my last post!  Since which I have:

* noticed a new flare star in Bootes (of which more anon)

* worked with undergrad students Erik Weiss and Amanda DeSouza on using current observations of accretion disk sizes as a function of wavelength to constrain their temperature profiles, and thought with grad student Laura Chajet about what might produce such profiles

* plugged away on the referee report for my paper on redshifted-trough BAL quasars (so close...)

* prepared observation templates for the Gemini 8-meter telescopes, did quick-look reductions on some spectra, and helped grad student Jesse Rogerson get started on real reductions

* taught astronomy

* helped write proposals for the Hubble Space Telescope and the Chandra X-ray observatory

* started thinking about proposals for Gemini and the 3.6-meter Canada-France-Hawaii Telescope

Back to work...