light curves

How the time flies.  Seems like yesterday (actually 2005) when the first observing proposals* for monitoring epsilon Aurigae were being submitted - and suddenly we have arrived at predicted mid-eclipse.  According to Jeff Hopkins, who has made a study of the light curves, he expected mid-eclipse to occur August 4th, 2010 = JD 2,455,413.

The light curve shows no strong evidence for "mid-eclipse brightening" thus far.  Now that epsilon Aurigae is getting well separated from the sun, airmass corrections are less a problem, so more accurate photometry is possible.  From Mt.Evans this week, we had an exceptional morning for J& H band work, very good signal to noise, but found the brightness was close to that reported during spring 2010 - well into totality.Read more

During the past week, careful observers have been struggling with the low horizon angle presented by epsilon Aurigae and its friends, due to approaching solar conjunction in early June.  Despite this, credible reports are being received that epsilon Aurigae may be as much as 0.1 mag brighter than it was during early May.  If you have a clear NW horizon and patience, try finding The Kids below Capella after sunset, and see if you can provide a brightness estimate during these challenging weeks of late spring.Read more

If you've tried to observe epsilon Aurigae lately, it is quickly sinking into the northwest at dusk, along with Orion and other winter constellations.  The star is at solar conjunction during early June, making observations more challenging over the coming several months.  To stretch the game analogy, it's essentially half-time - in terms off the eclipse schedule.  Naturally, this is just when the fabled mid-eclipse brightening is forecast to happen, suggestive of a central clearing in the midst of the dark disk.  Given the developments of the past months and the coming half-time show, it seems timely to review what's been learned, and outline some of the outstanding questions that further observations can help address. 

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Eyjafjallajokull may sound like a word lifted from Finnegans Wake (a novel by James Joyce), but the Icelandic volcano has grabbed worldwide attention by producing a dense ash cloud that threatens jet aviation over much of northern Europe again this week.  In this third blog exploration of the implication of direct detection of the disk in epsilon Aurigae, via interferometric imaging, I want to explore with you how terrestrial volcanic ash provides some analogies with the dusty material that scientists believe make up "debris disks" seen around a surprising percentage of normal stars. Read more

Observers are beginning to report a sea change.  Totality is upon us and the center of the dark turbulent disk is just about to make its presence felt atop the beacon of light that is the F star in epsilon Aurigae.

Photometrically, bumps and wiggles have persisted, a mix of out of eclipse variations and the stately progression of the eclipse itself.

Spectroscopically, the enhanced absorption of shell lines has been waxing and waning as though disk substructure is coming increasingly into view.  What we've been seeing is the "morning side" of the disk - the portion that has been facing cold space and is just starting to rotate toward the hot glare of the F star (7750K). As soon as we reduce this week's IRTF spectra, we'll share any info about changes detected in the near-infrared.Read more

It's December 8th evening, Julian Date (J.D.) 2,455,175 and we are only a few days from predicted time of Second Contact when total eclipse starts.

The words "1st, 2nd, 3rd, 4th contact" refer to moments when objects in eclipsing systems overlap partially and totally.  Consider a small circle crossing in front of a bigger circle: first, just the outsides touch (1st contact); then the small circle just gets fully inside the larger (2nd contact); later, the smaller circle begins to exit from inside the larger circle (3rd contact), and at the end, the circles stop touching at their edges, before separating (4th contact).Read more

Mid-November, ingress nominally 2/3 over, and the snows are arriving in the mountains.  We made one last attempt to reach Mt.Evans observatory on 14 Nov but huge drifts defeated the stout Unimog vehicles we used.  However, intrepid observers elsewhere are still getting peeks at the star, sometimes between clouds.  Some interesting trends are emerging since mid-October: the B filter photometry shows a decreased rate of decline, as does V filter (less so), but R and I filters appear to continue the decline in a linear fashion.  This means the star is relatively brighter in bluer wavelengths compared to redder ones - suggesting a hotter source - perhaps the F star pulsations continuing (like those seen pre-eclipse) and/or some of the supposed hot B star light is leaking out of the dark disk.  Richard Miles reports an ~0.1 mag jump in V-Ic after mid-Oct.Read more

There are hints in recent visual observations of a decline in brightness for epsilon Aurigae. In this walk through, learn how to read data and the light curve to make your own decision. What do you think? "Is it real, or is it Memorex?"

New to variable stars and wondering what a light curve is? Sadly, it's not a cool weapon from Star Wars (although I imagine Jedi would find them useful for fighting around corners). I've recently wrote a forum post describing light curves and how to read them. Check it out and post your questions and comments.