The Re-finding of Feige 85

by Doug Welch

Is there anything more lost than a star in a catalogue which can no longer be found? Such errant entries have been grist for the mills of all sorts of astronomical detective stories. The missing or mis-recorded entries span the range from the sublime to the ridiculous. For instance a whole cottage industry of speculation was introduced by Sirius being described as one of the “reddish” stars by Ptolemy in 150 AD, despite other earlier and contemporaneous records describing it as its more expected, and current, color white! The Flamsteed catalogue’s “missing in action” entries involved a record of the planet Uranus – pre-discovery. Amusingly, even Galileo recorded the planet Neptune as it passed close to the line of sight of his target-of-interest, Jupiter, on both Dec 28, 1612 and Jan 27, 1613 – more than two centuries earlier than its official discovery by Galle and d’Arrest on Sep 23, 1846.

But my story is much less impressive. It begins with the publication by Jacques Feige of the Mount Wilson and Palomar Observatories (as they were then known) of the Carnegie Institution of Washington, California Institute of Technology. At about the time the manuscript for this paper was being completed, I was being conceived – but that is another story!

Jacques Feige’s 1958 paper was entitled “A Search for Underluminous Hot Stars” and was published in the Astrophysical Journal, volume 128, pages 267 to 271. Faint blue stars might seem to be a fairly useless sub-group of observable objects, but it turns out that the inexorable influences of astrophysics conspire to make them a cornucopia of both astrophysical and practical interest.

On the astrophysical side, these objects end up being peculiar for a variety of reasons, including binary evolution, being examples of almost naked star cores left over from a stellar evolutionary event known as the Helium flash, being white dwarfs, being distant versions of main sequence stars which have no excuse for being as far away from the galactic disk as they are, or being members of a class of star known as sub-dwarfs. In a very real sense, every find is a winner!

What about the practical side? Certainly young, distant, blue stars could be found in or near the disk of the galaxy. But such stars were unusual at large angles to the Milky Way. In fact, a color image of stars in the direction perpendicular to the Milky Way would show that the overwhelming majority are yellow, orange, or reddish. Still, the few bluish objects (like QSOs) found in directions away from the plane of our galaxy were incredibly interesting. What’s more, when their colors were measured, they would need the instrument-to-instrument variations in sensitivity calibrated out. To do so, requires the measurement of “blue” objects, and this is where Feige’s catalog became so valuable. It was a list of the few relatively bright objects in those directions which were blue and had fairly featureless spectra. Hence, they became a set of very frequently used standard stars for both measurement of brightnesses and calibration of brightness versus wavelength.

Except that one of the 115 had gone “walkabout”. Feige 85 was listed as being at position 13 hours, 34.7 minutes of right ascension and +8 degrees, 35 arcminutes of declination for the 1950.0 coordinate frame. The brightness listed was 15.0 which was at the faint end of the stars listed in this catalog. And more importantly, it wasn’t there! Fortunately for our story, Jacques Feige published one other paper called “An Atlas of Identification Charts for 113 Blue Stars” in 1959 in the Astrophysical Journal, volume 129, page 600 which included 39!) “plates” – specially reproduced photographic images in the journal containing what we now refer to as “postage stamp” finder charts for the 113 stars (down from the originally-claimed 114 due to the Feige 33 apparently being identical to Feige 34, once a +1 degree error in declination was corrected!)

As Brian Skiff described it in an e-mail of Mar 20, 2010 to the aavso-discussion list “… Feige 85 is shown with approximate coordinates because the original position is greatly in error, and it is lost for now.”

Normally, that would be the end of the story since the sky is vast. But in the last few years an amazing project has emerged called astrometry.net. It has the simple goal of being able to take an image of a star field and give you back its location in the sky, image scale, rotation, and image flip, if any – *without any additional information*. Sounds hard and it is! Why bother? The answer is simple – the rate at which images come off survey telescopes is so high that it is impossible to give each one the TLC and human attention necessary to put each image on the proper “world coordinate system”. The solution *must* be automated. Enter astrometry.net whose folks have produced the indices and code to make this happen. All you need is an image to feed to the routine.

That is where the story of Feige 85 is somewhat unusual. Normally, lost stars in catalogues just have incorrectly-typeset coordinates and no finder chart. Feige 85 *had* a published image. In fact, sitting at my home computer on a weekend, I could download the published “plate” from the Astrophysical Journal almost instantly from the SAO/NASA Astrophysics Data System. The Adobe Acrobat Reader plugin in my browser displayed it, and I did a screen capture and saved the image. Then I used the image processing software GIMP to crop the image to hold only the field of Feige 85 and get rid of the corners outside the circular field. The scan of the finder chart was still pretty noisy, so I smoothed the image to make the stars more centrally-peaked and to sand the background into greater uniformity. A final inversion to the image was made to make the stars white and the sky dark.

The image was fed to the solve-field routine of astrometry.net. After a few CPU seconds, the image was “solved”. Feige 85 was at the position 13:36:21.2 +08:22:34 for equinox J2000.0. It had not been found in any other “hot star” list but was catalogued as 2MASS J13362125+0822335.

Thankfully, online versions of catalogues can be updated on the fly and Brian Skiff of Lowell Observatory saw to it that this was done in Simbad. He also noted that it appears that Feige’s error was 1 arcminute in RA (right ascension).

So, at last, the Feige catalogue can sleep the sleep of the scientifically just. In truth, it was a minor mystery, but it was fun! And it opened my eyes to the possibilities of working with older (and newer!) images in a different way.

The astrometry.net folks have suggested that star field images from plates and film might be precisely dated by identifying the brightnesses of known, regular variable stars. Then, these in turn could be used to fill in the historical lightcurves of any other variable stars in those images – whether or not they were known at the time. And of course, there are lots of other possibilities. The important thing is to recognize the power of new tools and to look at problems from new perspectives!

Links:
“Astrometry.net” http://www.astrometry.net/

“Astrometry.net: Blind astrometric calibration of arbitrary astronomical images” by Lang, D. et al.
The Astronomical Journal, Volume 139, Issue 5, pp. 1782-1800 (2010)
http://arxiv.org/abs/0910.2233
http://adsabs.harvard.edu/abs/2010AJ….139.1782L

“A Search for Underluminous Hot Stars” by Feige, J.
http://adsabs.harvard.edu/abs/1958ApJ…128..267F

“An Atlas of Indentification Charts for 113 Blue Stars” by Feige, J.
http://adsabs.harvard.edu/abs/1959ApJ…129..600F

“The field horizontal-branch B-type star Feige 86″
by Bonifacio, P., Castelli, F., and Hack, M.
Astronomy and Astrophysics Supplement, v.110, p.441
http://adsabs.harvard.edu/abs/1995A%26AS..110..441B

Podcast: Fun from the Sun

This month Michael (that’s me), Doug and Mike get together on Skype to discuss the Sun.

If I may have a moment, the Sun is unquestionably the most important thing in our universe. Every scrap of energy we have on this planet comes from the Sun. It’s big, bright and hugely important to the evolution of Man and our fate in the future. It’s also a cauldron of convecting plasma that behaves, in ways, like a big, boiling pot of water.

In the podcast we talk specifically about aurora and their source — sun spots, solar flares and coronal mass ejections. And we go off-topic and make jokes and stuff, too. An abbreviated version of this podcast is available at The 365 Days of Astronomy Podcast.

Enjoy now by subscribing to the podcast, downloading or listening now!

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This podcast is brought to you by Swinburne Astronomy Online, offering fully online degree programs in astronomy.

Cassini Images from this Weekend’s Enceladus, Tethys and Dione Flybys!

new pics from Saturn sys.

–Ben

Cassini Images from this Weekend’s Enceladus, Tethys and Dione Flybys!

August 14, 2010

Dear Friends and Colleagues,

Just down on the ground today … images from Cassini’s close flybys of Tethys, Dione and Enceladus this weekend.

Go to …

http://www.ciclops.org/view_event/140/Enceladus_Tethys_and_Dione_Rev_136_Raw_Preview

… and see some gorgeous raw images of these very different Saturnian moons.

Enjoy!

Carolyn Porco
Cassini Imaging Team Leader
Director, CICLOPS
Space Science Institute
Boulder, CO

http://ciclops.org

http://twitter.com/carolynporco

http://www.facebook.com/carolynporco

Life is common but time and distance too great

As I awed over another unbelievable Hubble image I couldn’t help but think the Universe is teeming with life. With billions of galaxies with billions of stars over billions of years — the math is undeniable: even the most unlikely situations will occur a great number of times. This is articulated mathematically with the Drake equation.

The problem is not the formation of life, it’s the unfathomable distances and spans of time between these formations. Science fiction has given us dreams of communicating and traveling over galactic distances. In reality, that is completely impossible given what we know about physics today. Utterly inconceivable. It’s a sad thought for the imaginative. If other life does exist in the Universe, we’d surely like to meet it. Dangers be damned, the thrill of finding other life is an undeniable quest and communicating with citizens of another an world would be an Earth- and life- changing event. But sadly, it will never happen. We are doomed to be alone.

While I’m not really that pessimistic it is a valid answer to the Fermi paradox. The reason we haven’t heard from any other of the vast numbers of alien civilizations out there is: it’s not possible. The laws of physics prevent it. Certainly some worlds are created within “view” of others and they enjoy (or suffer) the wonders of that interaction. But we were born alone and will die alone because we are too far away from our nearest galactic citizens. They’ll send messages and we’ll listen, and vice versa, but never at the same time or the same way.

I hope I’m wrong!

An “Island Universe” in the Coma Cluster

Nice eye candy.
–Ben

An “Island Universe” in the Coma Cluster

A long-exposure Hubble Space Telescope image shows a majestic face-on
spiral galaxy located deep within the Coma Cluster of galaxies, which lies
320 million light-years away in the northern constellation Coma Berenices.
The galaxy, known as NGC 4911, contains rich lanes of dust and gas near its
center. These are silhouetted against glowing newborn star clusters and
iridescent pink clouds of hydrogen, the existence of which indicates
ongoing star formation. Hubble has also captured the outer spiral arms of
NGC 4911, along with thousands of other galaxies of varying sizes. The high
resolution of Hubble’s cameras, paired with considerably long exposures,
made it possible to observe these faint details.

This natural-color Hubble image, which combines data obtained in 2006,
2007, and 2009 from the Wide Field Planetary Camera 2 and the Advanced
Camera for Surveys, required 28 hours of exposure time.

http://hubblesite.org/newscenter/archive/releases/2010/24/

meteorwatch.org

interesting site and tweet map.
–Ben

http://meteorwatch.org/

http://meteorwatch.org/meteor-map/#twitter-feed-map

Podcast: Lucas Macri on the Extragalactic Distance Scale

We have a new podcast on the feed and once again it is the extended version of our most recent contribution to The 365 Days of Astronomy Podcast. Michael Koppelman interviews Dr. Luca Macri of Texas A&M University about his work on the extragalactic distance scale.

You can subscribe with RSS and/or iTunes with the handy links on the right side of this page or download and/or Listen Now!
 

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This podcast is brought to you by Swinburne Astronomy Online, offering fully online degree programs in astronomy.

Dazzling Display of Promethean Force on Saturn’s F Ring

more cool ring structures.
–Ben
————————————-
July 20, 2010

Dear Friends and Colleagues,

Today, the Cassini Imaging Team is proud to release some outstanding new image mosaics and computer simulations of everyone’s favorite ring, Saturn’s F ring: the narrow, dynamic, and extraordinarily complex set of strands of ring material caught between the orbits of its shepherd moons, Prometheus and Pandora, a few thousand kilometers beyond the outer edge of Saturn’s main rings.

These new results, published last week in the journal Astrophysical Journal Letters, confirm what some of us veteran imaging scientists from the days of the Voyager mission long suspected: The F ring is the site of continual moonlet formation and, in most cases, eventual disruption. But what we didn’t know then was the exact mechanism by which this could happen.

Now we do, and the culprit is Prometheus and the particular sequence of steps that transpire in its repetitive disturbance of the F ring that creates clumps of ring debris.

And like so many of our most interesting results on Saturn’s rings, the tell-tale clues came in the form of shadows cast by these small, newly formed objects onto the faint, diffuse component of the F ring.

Go to …

http://www.ciclops.org/view/6367/Fan_in_the_F_Ring

… and see for yourself what Prometheus inflicts on the F ring. And be amazed at the complexity that is made possible by the simple force of gravity.

Enjoy!

Carolyn Porco
Cassini Imaging Team Leader
Director, CICLOPS
Space Science Institute
Boulder, CO

http://ciclops.org

http://twitter.com/carolynporco

http://www.facebook.com/pages/Carolyn-Porco/116163229386

Astrofest 2010

step away from the computer and go ‘LOOK’ at something.
–Ben

================================
from : Jim Cuca wglogowski@gmail.com

Dear astronomy enthusiast:

The Chicago Astronomical Society invites you to attend our annual star party, Astrofest, which will be held September 10-11, 2010 at Vana’s near Kankakee, Illinois. Registration forms and related information are available at

http://www.chicagoastro.org/index_files/Page345.htm

The theme for this year’s event is “The Link Between Astronomy and Particle Physics.” In addition to our usual line-up of astronomers, Astrofest 2010 will include presentations by scientists involved in research into such contemporary topics as dark matter and dark energy. Our star party will be held on Vana’s 20+ acre field, with plenty of room for camping and telescopes; each attendee will be invited to use our 14-inch observatory telescope. Other activities include: astrophotography contest; telescope contest; door prize raffle.

We hope to see you at Astrofest 2010.

If there are any questions, please contact

Jim Cuca at jamescuca@comcast.net.

OSTP to Co-Host “Astronomy Night on the National Mall”

another astro event in DC.

WOW!

–Ben

OSTP to Co-Host “Astronomy Night on the National Mall”

OSTP, in conjunction with Hofstra University, will co-sponsor a free, open to the public star party July 15 on the National Mall in Washington, DC.

If you are near the DC area in come enjoy close-up views of the crescent Moon, Venus, Mars, Saturn, star clusters, and nebulae. You can even gaze at our own Sun early in the evening with the help of specially filtered telescopes. “Astronomy Night on the National Mall” will go from 6 p.m. to 11 p.m. on Thursday, July 15 (with a July 16 rain date). Telescopes, posters, and video equipment will be set up just northeast of the Washington Monument, between 14th and 15th Streets NW, and Madison Drive and Constitution Ave. View a map of where Astronomy Night on the Mall will be held…

http://www.whitehouse.gov/blog/2010/07/03/ostp-co-host-astronomy-night-national-mall