north central florida’s may/ june amateur astronomy club … · mer observing almost any...

First Light May / Jun / 2011 1/ 28

North Central Florida’s Amateur Astronomy Club 29°39’ North, 82°21’ West

May/ June Issue 104.1/106.1

Member Astronomical League

Member International Dark-Sky Association

On June 15, 2011 the totally eclipsed Moon was very dark, with the Moon itself positioned on the sky toward the center of our Milky Way Galaxy. The red lunar disk lies in the constel-lation Ophiuchus near the border with Scorpius and Sagittarius. As seen on Astronomy Pic-ture of the Day (June 17, 2011) the dark of the eclipsed Moon competes with the Milky Way's faint glow. Copyright: Babak Tafreshi/Dreamview.net

2 / 28 May / Jun 2011 First Light

HAM RADIO and ASTRONOMY I’ve been a HAM radio operator for almost as long as I have been interested in Astronomy. Both hobbies are intertwined in my life. In fact, most people in HAM radio don’t know me by my Surname, but my FCC call sign: W4GJ . When I am introduced at HAM radio conventions or club meetings, I’m “Bob W4GJ,” not “Bob Lightner.” There are thousands of us who are involved in ra-dio astronomy in one way or another. One of the obstacles to getting involved in this aspect of the two hobbies is that

radio astronomy deals with the RF portion of the electro-magnetic spectrum, as opposed to the visible light portion that our optical brothers and sisters work with. This requires the radio tele-scope owner to deal with enormous apertures as compared to optical ones with the same spatial resolution. Big size usually equates to big cost. Another drawback is that the radio sky is gener-ally faint and somewhat uninteresting as compared to the visible sky. Expensive highly sensitive receivers and big antennas are usually required of the radio astrono-mer observing almost any celestial object.

K3PGP Antenna HB9Q Antenna I’m a member of three sub-groups of radio astronomy and HAM radio, SARA, AMSAT and Cube-Sat. The Society of Amateur Radio Astronomers (SARA) is an international society of dedicated en-thusiasts who teach, learn, trade technical information, and do their own observations of the radio sky. This organization is a scientific, non-profit group founded for the sole purpose of supporting amateur radio astronomy. SARA was organized in 1981, and today has hundreds of members worldwide. The group consists of optical astronomers, ham radio operators, engineers, teachers and non-technical persons. Many of our members are new to the field, and membership is extended to all who have an interest in radio astronomy. The Radio Amateur Satellite Corporation (as AMSAT is officially known) was first formed in 1969 as an educational organization. Its goal was to foster Amateur Radio's participation in space re-search and communication. AMSAT was founded to continue the efforts, begun in 1961, by Pro-ject OSCAR, a west coast USA-based group which built and launched the very first Amateur Ra-dio satellite, OSCAR, on December 12, 1961, barely four years after the launch of Russia's first Sputnik.

Presidential Comments AAC President Bob Lightner


Today, the "home-brew" flavor of these early Amateur Radio satellites lives on, as most of the hardware and software now flying on even the most advanced AMSAT satellites is still largely the product of volunteer effort and donated resources.

Phase 3 E Satellite Eagle Satellite For over 42 years AMSAT groups in North America and elsewhere have played a key role in significantly advancing the state of the art in space science, space education, and space technology. Undoubtedly, the work now being done by AMSAT volunteers throughout the world will continue to have far-reaching, posi-tive effects on the very future of both Amateur Radio, as well as other governmental, scientific and com-mercial activities in the final frontier. Rarely have a group of "amateur" volunteers managed to do so much...for so many...with so little. CubeSat is a relatively new and exciting activity that is an international collaboration of over 40 universi-ties, high schools, and private firms developing picosatellites containing scientific, private, and government payloads. A CubeSat is a 10 cm cube with a mass of up to 1 kg.

CubeSat Constructed CubeSat Kit One additional aspect of HAM radio and astronomy is EME communications. Some HAM operators enjoy bouncing signals off of the moon and speaking to other HAMS across the globe.


DL7APV E-M-E Antenna

Did you know that most astronauts and cosmonauts are licensed HAM radio operators? Yes, in fact there have been HAM stations set up on the MIR, SpaceLab and on the ISS. Each Space Shuttle flight had a HAM station that astronauts used to talk with HAMs down on the earth.

Tracy Caldwell, KF5DBF OWEN GARRIOTT, W5LFL There is practically no limit when you merge two hobbies together. I have spoken to eight orbiting HAMs and even had EME contacts. During the 40th anniversary of the Apollo 11 mission, I spoke to my HAM friends down in Arecibo (their antenna was a little larger than mine) but it was fun chatting with them using moon-bounce on 1296 MHz. HAM radio operators are also heavily involved in the Search for Extraterrestrial Intelligence (SETI). You don’t have to be a licensed HAM operator to get involved in this effort (since it’s receive-only)! When I was an astronomy student at the UF many years ago, I helped build 640 dipole antennas for Dr. Carr which were installed at the UF’s Radio Observatory, west of Gainesville near Old Town. We used these antennas to listen to the Jupiter-Io emissions on 26.3 MHz.


Dipole Antenna Farm at UFRO in 1969

Some HAM operators enjoy talking to other HAMS by bouncing their signals off of the ionized trails made by meteors entering our atmosphere…NOW THAT’S PRETTY AMAZING, HUH?! One of the major contributions to astronomy is when amateur radio astronomers monitor the intensities of many variable sources such as quasars and pulsars. Valuable as such work is, the task is not easy. For example, active galaxies have their intrinsic radio variability at very short wavelengths (in the centimeter or millimeter region of the spectrum). This usually means that the amateur needs an expensive antenna be-cause, like an optical telescope, the radio variety must have a surface shape that is extremely precise to much better than the wavelength of the radiation being observed. Add to that the fact that extragalactic radio sources generally weaken at these shorter wavelengths which require VERY LARGE antennas and super sensitive receivers. But with today’s software, many of the receiver problems can be overcome. Pulsars are not very bright. Additionally the accurate timing needed to correctly identify their “glitches” (sudden changes) in their rotation rates comes at a high cost. If amateur radio astronomers can overcome these major obstacles they might eventually organize a monitoring network similar to the Ameri-can Association of Variable Star Observers (AAVSO). Believe it or not, amateurs have one slight advantage over professionals. We can cover large areas of the sky whereas instruments like the professional Very Large Array (VLA) and others are limited with a nar-row field of view. Amateurs can also undertake longer-term observations where professionals are fighting for time on an instrument. Hence a small dust-covered object in the Milky Way that suddenly supernovas is more likely to be discovered by an amateur than a professional. 73, Bob W4GJ


STAR PARTY / OBSERVATION SCHEDULE: Upcoming Events - 2011

Event

Date

Location Start/End Time

Summer Solstice Moon Party!

Saturday, June 18 Newberry Star Park Sunset approx 8:31 pm ET

Full Moon Madness! Saturday, July 16 Newberry Star Park Sunset approx 8:32 pm ET

Perseid Meteor Party Saturday, August 13 Loftus Family Farm Sunset approx 8:12 pm ET

SPECIAL EVENTS - 2011 See the AAC website for details

Event

Date

Location Check the website for directions Start/End Time

N/A N/A N/A N/A

Messier Marathon. Image Credit & Copyright: Babak Tafreshi (TWAN). Explanation: In this action scene, red night vision lights, green laser pointers, tripods and telescopes in faint silhouette surround intrepid sky gazers embarked on the 10th annual Iran Messier Marathon.


Alachua Astronomy Club, Inc. 2011 Officers President: Bob Lightner Phone: 352-373-3055 Email: [email protected] Vice-President: Marlene Grabbe Phone: 352-732-2767 Email: [email protected] Treasurer: Ivo Rabell Phone: (352) 665-9381 Email: [email protected] Secretary: Paula McLain Email: [email protected] Board of Directors

Howard Eskildsen Bill Helms Pamela Mydock Chairs and Committees:

Star Parties: Paul Griffin Email: [email protected] Programs/Promotions: Andy Howell Phone: (352) 505-4852 Email: [email protected] Outreach Coordinator: Mike Toomey School Liaison & Outreach: Tandy Carter Email: [email protected] ATM SIG: Chuck Broward Phone: 352-373-7527 Email: [email protected] Astronomical League Correspondent: Charles S. Broward Phone: 352-373-7527 Telescope Custodian: vacant Email: [email protected] Lunar Observing/SIG: Bob O’Connell Phone: 352-475-1586 Email: [email protected] Webmasters: vacant Email: [email protected] FirstLight Editor: Arne Reykowski Phone: 352-562-3387 Email: [email protected]

Submitting Articles to FirstLight The AAC encourages readers to submit articles and letters for inclusion in FirstLight. The AAC reserves the right to review and edit all articles and letters before publication. Send all materials directly to the FirstLight Editor. Materials must reach the FirstLight Editor at least 30 days prior to the publication date.

Submission of articles are accepted by e-mail or on a CD. Sub-mit as either a plain text or Microsoft Word file. (In addition, you can also send a copy as a .pdf file but you also need to send your text or Word file.) Send pictures, figures or diagrams as separate .gif or .jpg file. Mailing Address for Hard Copies or CDs Note: Since our mailbox is not checked daily, mail materials well be-fore the deadline date. (Hence, submission by e-mail is much pre-ferred!) c/o FirstLight Editor The Alachua Astronomy Club, Inc. P.O. Box 141591 Gainesville, FL 32614-1591 USA By E-Mail: Send e-mail with your attached files to [email protected]. FirstLight is the bi-monthly publication of the Alachua Astronomy Club, Inc., Gainesville, Florida. © Copyright 2011, Alachua Astronomy Club, Inc. FirstLight is copyright by the AAC. No part of FirstLight may be reproduced by any means, nor stored in retrieval systems, transmitted or otherwise copied without written permission from the AAC.

AAC Meeting Location - AAC regular meetings are held on the second Tuesday of each month at 7:00 p.m. at the Florida Museum of Natural History, Powell Hall, in the Lucille T. Maloney Classroom, on UF campus, unless otherwise announced. All meetings are free and open to the public. Join us for some great discussions and stargazing afterwards. Please visit our website for more information (floridastars.org). There is no monthly meeting in December.


We have two new Web Smiths for the AAC: Byron Bergert and Daniel Wells. The new Web page upgrade is just about to be unveiled (finally) and we hope that we will be able to quickly adapt to a new Web presence.

In addition, we have a new Star Party Coordinator; Paul Griffin.

Please thank these three new volunteers and lend them your patience and sup-port as they carry on their new positions in our club.

AAC Club News:


Across: 2. This man lost his nose in a student duel over who was the superior mathematician 4. In 1543 while on his deathbed this man published his theory that planets orbit around the sun 7. In 1846 this man was the first to spot the planet Neptune 8. In 1666 this man began his work on the theory of universal gravitation 11. In 120 B.C.this man completed the first known catalog of the stars 12. In 1705 this man predicted that a great comet would return to the skies in 1758 Down: 1. In 1923 this man proved that other galaxies lie beyond the Milky Way 3. In 1916 this man first proposed the General Theory of Relativity 5. In A.D. 150 this man published his theory of the earth cen-tered universe. 6. In 1842 this man discovered the principle by which sound or light shifts in frequency or wavelength due to the motion of its source with respect to the observer 7. In 1609 this man discovered craters on the moon and made other observations with a new scientific device 9. In 1930 this man discov-ered Pluto 10. This man developed two important laws of motion around 1620 and a third law of planetary dynamics 11. In 1781 this man discovered the planet Uranus.


Minor Planets FirstLight Editor Arne Reykowski

You have seen Venus, Mars, Jupiter, Saturn and even honed in on Mercury, Uranus, and Neptune? And now you are looking for some new challenges? Try a minor planet for a change! At opposition, some of these objects rival Uranus and Neptune in brightness. However, due to their closer proximity to Earth, they seem to be moving faster across the sky than those distant planets. For starters, Vesta, with an opposition magnitude of 5.6 is a perfect object for small instruments, barely beyond un-aided visual detection. Attached is a finder chart for Vesta which approaches opposition in early August. As an alternative to visual observations, a relatively short exposure with a digital camera can capture such

an object too. Repeated observations / re-cordings should identify these fairly rapid moving objects over the course of days and weeks. For more information, follow the link for the Brit-ish Astronomical Association below. Happy Hunting! http://britastro.org/computing/handbooks_charts.html

60 Echo 2011 Jun 25 12.0

194 Prokne 2011 Jun 26 10.6

511 Davida 2011 Jun 26 11.5

43 Ariadne 2011 Jun 27 9.0 21 Lutetia 2011 Jul 4 9.4 32 Pomona 2011 Jul 9 10.9 185 Eunike 2011 Jul 15 11.6

704 Interamnia 2011 Jul 18 10.0

2 Pallas 2011 Jul 29 9.5 4 Vesta 2011 Aug 5 5.6 1 Ceres 2011 Sep 16 7.6

Name Opposition Opp. Magnitude


I am sure you heard this question before at a star party: How far can you see with your telescope? Usually, I end up explaining that it is the brightness and not the distance of an object that matters. But then, on a recent flight back from Europe, I was reading “Sterne und Weltraum”, the German equiva-lent of Sky & Telescope. It contained an article about the Quasar 3C 273. This object is located in the constellation Virgo and has an approximate magnitude of 12.8. This puts it in the observable range for larger amateur instruments like 8 inch Schmidt-Cassegrains. Quasars belong to the brightest objects in the observable Universe. Unfortunately, most of them were formed in the early Universe which places them far away in space and time, out of reach for amateur in-struments. The Quasar 3C 273 however, is a an exceptionally close object at a distance of “only” 2 Billion light years. So there you have it: How far can you see? 2 Billion light years! Check out the following links: http://en.wikipedia.org/wiki/3C_273 http://washedoutastronomy.com/content/3c-273-quasars-are-easy

How Far Can you See? FirstLight Editor Arne Reykowski

This finder chart shows the location of 3C 273 in Virgo. For more detailed information on how to find this Quasar, refer to the links above.

The image here was obtained with the 4-meter Ma-yall telescope of Kitt Peak National Observatory (credit: AURA/NOAO/NSF) and is copyrighted. For details and a hi-res version of this image, see NOAO's 3C273 page.


July Club Meeting

Date and Time: TUESDAY, JULY 12, 2011, 7:00 p.m. ET

Speaker: Michael S. Generale, NASA Test Director at Kennedy Space Center.

NASA Update: Status of Space Shuttle Atlantis mission & the Orion Multi Purpose Crew Vehicle Location: Powell Hall, Florida Museum of Natural History (Lucille T. Maloney Classroom), UF Campus, Gainesville FL

Great Links: http://www.solarsystemscope.com/ SOLAR SYSTEM SCOPE SSS is Flash based 3D model of Planets of Solar System and the Night Sky. http://www.zooniverse.org/ The Zooniverse is home to the internet's largest, most popular and most successful citizen sci-ence projects. Hunt for Planets, classify Galaxies, count Lunar craters and many more. These are real online science projects. From the comfort of your living room you can help researchers in their efforts to understand the Universe around us.


Carrington Rotation 2110 Report Howard Eskildsen

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Pelican Nebula AAC Club Member Web Master Byron Bergert

The Pelican Nebula IC5070 and IC5067 Astrophoto by Byron Bergert

The constellation Cygnus sometimes referred to as the Northern Cross is again visible in the early morning sky. The Pelican Nebula is an H II re-gion near the North American Nebula and the bright star Deneb. This im-age was made using an Apogee U8300 camera on a Takahashi FSQ106EDX telescope. The total exposure was eight hours over 4 con-secutive nights using L, R, G, B and Hydrogen alpha filters. From Wikipedia, the free encyclopedia: The Pelican Nebula (also known as IC5070 and IC5067) is an H II re-gion associated with the North America Nebula in the constellation Cyg-nus. The nebula resembles a pelican in shape, hence the name. The Pelican Nebula is a large area of emission nebula in the constellation Cygnus (the Swan), close to Deneb, and divided from its brighter, larger neighbor, the North America Nebula, by a molecular cloud filled with dark dust.

The Pelican is much studied because it has a particularly active mix of star formation and evolving gas clouds. The light from young energetic stars is slowly transforming cold gas to hot and causing an ionization front gradually to advance outward. Particularly dense filaments of cold gas are seen to still remain. Millions of years from now this nebula might no longer be known as the Pelican, as the balance and placement of stars and gas will leave something that appears completely different.


A very negative outlook for Florida in 2011

with some hope for 2012 if one is willing to travel Did you read or hear about the total lunar eclipse of this past June 15th? This lunar eclipse was one of the longest in recent times (totality lasted 100 minutes). Did you then go out in the evening and nothing happened to the Moon? Don’t fret. This eclipse was visible nearly worldwide except for people in North or Central America, and Ant-arctica! Normally four eclipses occur each year, two of the Sun and two of the Moon. However, 2011 is unusual with six eclipses—four solar and two lunar: Jan. 4: Partial solar eclipse Jun. 1: Partial solar eclipse Jun. 15: Total lunar eclipse July 1: Partial solar eclipse Nov. 25: Partial solar eclipse Dec. 10: Total lunar eclipse Surprisingly, none of the first five eclipse paths run through the lower forty-eight and little of the last eclipse is visible from Florida. During the last eclipse of this year, the Moon will enter Earth’s lighter penumbal shadow during morning twilight in Gainesville. But, the Moon will only be about seven degrees above the western horizon. Thus, the Moon will set well before entering the darker umbral shadow as the sky bright-ens from the morning Sun. From a practical point of view, this eclipse will go unnoticed in the eastern USA. So Florida misses out in 2011. What about 2012? The usual frequency of only four eclipses per year occurs on the following dates: 2012 May 20: Annular solar eclipse 2012 June 4: Partial lunar eclipse 2012 Nov. 13: Total solar eclipse 2012 Nov. 28: Penumbral lunar eclipse Notice that separations between solar-lunar eclipse pairs are approximately a half lunar period or about two weeks. This is normal. Sadly, next year also brings “eclipse doom” for our state. None of the four 2012 eclipses are again favorable for Florida. Both 2012 solar eclipses are not visible from Florida including their partial phases. The 2012 November penumbral lunar eclipse is also not visible from here.

Upcoming Eclipses AAC Club Member Howard L. Cohen


Lastly, a small part of the 2012 June 4th partial lunar eclipse is technically visible from Florida. However, the Moon will enter the Earth’s umbra at only six degrees above the western horizon as the morning sky brightens. This occurs only about one-half hour before sunrise. However, if willing to travel, one can see the entire annular phase of the 2012 annular solar eclipse of May 20th from the western USA. Here, annularity will last more than four minutes. The path of the annular eclipse runs from northern California into southern Nevada, southwest Utah, northeast Arizona through central New Mexico, and ultimately ends in the western Texas panhandle. During an annular solar eclipse, the Moon’s disk is not large enough to cover the entire solar disk leaving a ring or annulus of sunlight around the Moon’s edge. Although annular eclipses do not measure up to the grandeur of total solar eclipses (e.g., the Sun’s corona is not readily visible), they are still one of nature’s striking events. I plan to observe this eclipse from Arizona where weather prospects are very good. In addition, sixteen days later, inhabitants of the western USA can also see Venus transit (cross) the Sun’s disk (June 5th). This is the last time a transit of Venus will occur in our lifetimes since the next such transit is not until 2117! Don’t miss this extraordinary, historical event. Plan to tour the Southwest as I will and stay to see the transit. Yes, the beginning stages of the transit of Venus will be visible in Gainesville as the Sun descends toward the western horizon from an altitude of 20 degrees. Still, the Sun will set before maximum transit, which occurs about one hour after sunset. (The entire transit lasts nearly seven hours.) Un-fortunately, late afternoon June thunderstorms in Florida could hide the entire event. Then more than a century will pass before you can next see this rare phenomenon. I repeat. Go to the south-western USA to see more of the transit—until about one hour after maximum—and where weather prospects are again very good. Later in the year, in November, a total eclipse of the Sun occurs (November 13 or 14 de-pending on your location). Nevertheless, no part of North America will see this event even as just a partial eclipse. Still, anyone who wants to experience one of nature’s greatest spectacles, can travel to northeastern Australia or South Pacific ocean locations east of Australia. Details about this eclipse and a tour I will be helping escort to Australia for this eclipse are at astroadven-tures.net. A reminder: For anyone unable or willing to travel to see a total solar eclipse, the next for the USA is not until August 2017. In this country, the total eclipse path will run a southeasterly course from Oregon through South Carolina. Again frequent summer storms may hinder seeing this eclipse with best weather prospects, as before, in some western states. No one ever said observational astronomy would be convenient or easy! ___________________________________________________________________________ Howard L. Cohen is an emeritus professor in the University of Florida's Department of Astronomy and a founding member of the Alachua Astronomy Club, Inc.


Florida June 14th 2011 FirstLight Editor Arne Reykowski

Image: USDA Forrest Service—Remote Sensing Center. http://activefiremaps.fs.fed.us/ If aliens would have caught a glimpse of Florida this day, they could have identified several large fires with clouds extending several hundred miles. There was so much smoke in the air that the moon appeared strangely orange in the Gainesville sky that night, akin a total lunar eclipse. One of the fires on this map near Keystone Heights actually encroached on the property of Bob O’Connell.


AR1236 with Lightbridge Howard Eskildsen Board Member

Image taken: June 17, 2011, Ocala, Florida, USA Excellent seeing allowed detailed imaging of AR 1236 with associated plage and a light bridge crossing the large, proceeding spot. Orion 80mm ED refractor. Ca-K im-age with Lunt B600 Ca-K Module. DMK 41AU02.AS imager. Date and time on pho-tos. The nature of light bridges is not fully understood. They often herald the break-up of a sunspot. Some research suggests that magnetic fields at the base of a light bridge are busy cross-crossing and reconnecting--the same explosive process that sparks solar flares. Does this mean the primary core of sunspot 1236 will explode? Or quietly fall apart? No one can say. (See also Spaceweather.com from June 18, 2011)


R Coronae Borealis Prepared by Kate Davis, AAVSO Technical Assistant, Web - January 2000

The Enigmatic R Coronae Borealis...

There too that Crown which Bacchus set on high, A Brilliant sign of the lost Ariadne. - Aratos

"The variable star R Coronae Borealis is a jewel worthy of a place in any crown. It is one of the most interesting and most peculiar of all variables, and is often called the 'ideal' irregular variable. Its times of minima are distributed absolutely at random, according to the laws of pure chance" (Margaret Mayall, The Review of Popular Astronomy, May/June 1962, p33).

R CrB finder chart.

R Coronae Borealis (R CrB) has been a favorite with observers ever since its discovery nearly 200 years ago by the English amateur, Edward Pigott.

Located inside the bright circlet of stars that form the Northern Crown, R CrB is usually easy to find with binoculars or even the unaided eye at 6th magnitude.

Variable Star of The Month Programs/Promotion Andy Howell


The critical contribution that amateurs have made to astronomy by observing R CrB is articulated on the ISO (Infrared Space Observatory)/ESA (European Space Agency) 12 June, 1996 informa-tion note page and is quoted below. The ISO homepage may be located at http://www.iso.vilspa.esa.es/. The ESA homepage may be found at http://www.esa.int/.

Image of the Infrared Space Observatory

"We caught this star smoking," says Helen Walker of the Rutherford Appleton Laboratory in Eng-land, who was in charge of the observation. "The amateurs saw the star fade from view in visible light in October, but it remained bright in the infrared. The telltale wavelengths revealed sooty car-bon compounds newly formed in the star's vicinity. Without ISO [and amateur astronomers] we could not hope to analyse such a striking event."

R CrB is currently recovering from a period of fadings that started in August of 1999. The AAVSO encourages observers to monitor this elusive star and report their observations to headquarters. For more information on submitting observations, visit our Observer's page.

Year


A Look at the Light Curve

R Coronae Borealis is the prototype star of the R Coronae Borealis (RCB) type variables. These hydrogen-deficient and carbon-rich F or G supergiants go into "outburst" not by brightening like other variables, but by fading!

R CrB spends most of its time at maximum around magnitude 6, and at irregular intervals it ex-periences deep declines of up to 8 magnitudes. The decline is sharp. It may drop several magni-tudes in a few weeks. The star may remain faint for an extended period of time or have several recoveries and declines in succession. Often the final rise back to maximum light is slow, taking several months to a year.

Right now the AAVSO has a copy of the R Coronae Borealis monograph on sale for you. The Monograph contains a light curve of R CrB from 1843 to 1990, and with your monograph order, you will receive a free supplement that updates the light curve to 1995. To obtain a copy of the R Coronae Borealis light curve from 1843 until 1995, visit our online store.

A Look at R CrB

R Coronae Borealis is an unusual star worthy of much attention, observation, and research. This abstract from Geoffrey C. Clayton's Invited Review Paper, "The R Coronae Borealis Stars", Publi-cations of the Astronomical Society of the Pacific, 108, 1996 March, gives us a clue why these stars are so interesting:

This year [1996] marks the bicentennial of the discovery of the variability of R Coronae Borealis. The R Coronae Borealis (RCB) stars are distinguished from other hydrogen-deficient objects by their spectacular dust-formation episodes. They may decline by up to 8 magnitudes in a few weeks, revealing a rich emission-line spectrum. Their atmospheres have unusual abundances with very little hydrogen and an overabundance of carbon and nitrogen. The RCB stars are thought to be the product of a final helium shell flash or the coalescence of a binary white-dwarf system. Dust may form in non-equilibrium conditions created behind shocks caused by pulsations in the atmospheres of these stars. The RCB stars are interesting and important, first because they represent a rare, or short-lived stage of stellar evolution, and second because these stars regularly produce large amounts of dust so they are laboratories for the study of dust formation and evolution.

What is Happening?

R Coronae Borealis stars stay at maximum and then intermittently experience fluctuating minima because carbon-rich dust clouds periodically obscure the photosphere of the star. R Coronae Bo-realis, when exposed, is a star that usually shines around 6th magnitude, and it is during this time that the star is at "maximum". At highly irregular time intervals that are unpredictable as of yet, the star enters a deep minimum. The minimum is caused by a dust cloud of amorphous carbon (extinction curves have confirmed that the dust causing the decline is carbon-rich), which eclipses the photosphere of R CrB, preventing an observer from seeing the entirety of the star's luminos-ity. Each successive drop in brightness within a decline is caused by new dust formation. These episodes of dust formation seem to occur on successive pulsational cycles of the star, although this is hard to prove. There are different explanations of the formation and evolution of the dust clouds and it is not quite predictable yet when, why, or how they form. Eventually, the dust cloud moves out of the way, re-exposing the photosphere of the star as it returns to "maximum".


Two Theories on Dust Formation

One theory that explains the formation of dust clouds around RCB type stars has been called the Orbiting Dust Cloud Theory. This model, as explained in Geoffrey C. Clayton's Invited Review Pa-per "The R Coronae Borealis Stars", PASP, 108, 1996 March, proposes that clouds of dust orbit the RCB star and periodically pass along the line of sight of the star, obscuring its photosphere. This model, however, has trouble fitting the observational data. The passage of a dust cloud across the star is not consistent with the structure of the decline light curve or with evidence of dust-grain evolution. So dust ejection from a secondary star in a binary system must be invoked to make this model viable, however, there is no evidence of binarity in RCB stars.

A second, more likely model explained in the same article by Geoffrey C. Clayton involves dust forming from material lost from the RCB star itself. Mass is lost from the RCB star and then moves away from the star until it reaches the condensation temperature of carbon dust (at about 20 stellar radii). Once the carbon dust has formed, the photosphere of the star is eclipsed, the star goes into minimum, and emission lines appear. When the dust is blown away by radiation pressure the photosphere of the star may again be seen. This model, dubbed the Dust Puff The-ory, is a good one except that it implies a physical connection between the stellar atmosphere and the location of the dust formation (which is hard to imagine for dust forming at 20 stellar ra-dii). One way to avoid this problem is to say that the dust forms closer to the star and is blown away by radiation pressure. But then one might expect and rightly so, assuming thermodynamic equilibrium, that the region very near the star is too hot to enable the condensation of carbon into dust.

Even now, after over two centuries of observation, many aspects of the RCB phenomenon re-main mysterious, including the details of the dust formation mechanism, the evolutionary status of RCB stars, and the nature of their emission-line regions.

For More Information

The Myths of Corona Borealis

The R Coronae Borealis Stars, by Geoffrey C. Clayton, an Invited Review Paper, Publications of the Astronomical Society of the Pacific, 108, 225-241, 1996 March.

"Model for R Coronae Borealis Stars", Barbara A. Whitney, Noam Soker, and Geoffrey C. Clay-ton, Astronomical Journal, 102, 284-288, 1991 July.

Observations of R Coronae Borealis Stars in Decline: Empirical Arguments for Dust Formation near the Stellar Surface, Geoffrey C. Clayton, Barbara A. Whitney, S. Adam Stanford, and John S. Drilling, The Astrophysical Journal, 397, 652-663, 1992 October.

AAVSO Monograph 4, Light Curves of R Coronae Borealis 1843-1990

AAVSO Monograph 4, Supplement 1, Light Curves of R Coronae Borealis 1991-1995


*AAVSO Special Notice #241* *June 3: *A new supernova in M51 was discovered by A. Riou and confirmed by several sources, including the Palomar Transient Factory (Silverman et al., ATEL 3398). It is located at 13:30:05.08 +47:10:11.2 J2000 and has a magnitude of about 13.5. Nice images of the super-nova can be found at: http://6888comete.free.fr/fr/imageSN.htm. PTF also obtained a spectra from Keck, indicating that this is a type II supernova with a relatively blue continuum with P-Cygni profiles in the Balmer series. This is a unique event, because it occurs in a galaxy that is imaged almost constantly. There must be many photos available that show the rise of this SNe, so the data-mining opportunity is obvious. It is transiting at local twilight and should be observable for northern hemisphere observers for several months. A new APASS sequence should be uploaded soon. We recommend taking nightly monitoring images in B and V for CCD observers, along with visual estimates, until the supernova is no longer visible. Here is an excuse to take the 10 millionth image of M51! - Arne Henden, Director, AAVSO The supernova is currently magnitude 12, visible in 8-inch telescopes. Attached is a finder chart with comparison star magnitudes shown (decimal points omit-ted). See also next page taken from Astronomy Picture of the Day, June 11, 2011.

New Supernova in M51 Programs/Promotion Andy Howell


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Space Shuttle Rising Credit: NASA

Explanation: What's that rising from the clouds? The space shuttle. If you looked out the window of an airplane at just the right place and time last week, you could have seen something very unusual -- the space shuttle Endeavour launch-ing to orbit. Images of the rising shuttle and its plume became widely circulated over the web shortly after Endeavour's final launch. The above image was taken from a shuttle training aircraft and is not copyrighted. Taken well above the clouds, the image can be matched with similar images of the same shuttle plume taken below the clouds. Hot glowing gasses expelled by the engines are visible near the rising shuttle, as well as a long smoke plume. A shadow of the plume appears on the cloud deck, indicating the direction of the Sun. In the meantime, Endeavour has completed its 16 day mission and safely returned to Cape Canaveral. (Credit: NASA, Bill Ingalls)

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