Double Dipping: Spring 2010

Variable Stars Near Deep Sky Treats

March is typically the time of year observers take on the challenge of the Messier Marathon. The Messier Marathon is an attempt to view all 110 Messier objects in one night, and it takes the entirety of a night to achieve it. You have to start as early as you can, to get the first few objects, as Cetus and Pisces are setting, and the last few objects in Aquarius and Capricorn are a challenge, even if you�ve managed to say fresh after a whole night. I personally have never completed the marathon, and I can�t say I know anyone who has actually done it.

The important thing for this piece is that as warmer spring temperatures arrive, there is no shortage of deep sky treats to keep your friends and relatives entertained. Meanwhile, you and I will figure out how to squeeze in some variable star observing in between galaxies, nebulae and star clusters. It will be a bit of a challenge at this time of year because there just aren�t that many stars in the sky. As fate would have it, in spring the plane of the Milky Way lines up pretty closely with the horizon in early evening. So we don�t see the fullness of the galaxy in the sky. Instead, everywhere we look we are looking out into deep space, away from the center or arms of the Milky Way.

We ended our winter tour in Orion, so we�ll head east and start with the brightest star in the sky, Sirius. Glowing at magnitude -1.08, alpha Canis Majoris is a blinding object in a telescope. 8.5 arc minutes southeast, embedded in the glare from Sirius, is the UGZ type variable, HL CMa. Ranging from magnitude 10-14.5, it is an active, unpredictable star that is visible most of the time in 10� or bigger scopes. Four degrees south of Sirius is the beautiful star cluster, M41. It contains about 100 stars, including several red giants, the brightest glowing at magnitude 6.9, and situated near the cluster's center.

Heading north into Monoceros, we are going to luck out and observe two nebulae that have variable stars embedded inside them. It doesn�t get any easier than that. Two for one, two times in one constellation!

NGC 2346 Credit: NASA and STScI 

First on the tour is NGC 2346 also known as Butterfly NGC 2346. Discovered by William Herschel in 1785, NGC 2346 is fairly conspicuous and has been extensively studied. Among its most remarkable characteristics are, its unusual butterfly shape, and its unusually cool central star, V651 Mon, which varies irregularly from 11.3 � 15.3.

The variable is a spectroscopic binary and has a period of about 16 days. Variability is probably due to clouds of dust in orbit around the binary. As this dust is heated by the central star it glows brightly in the infrared.

The evolutionary track taken to create this dusty, double variable system is pretty interesting. Millions of years ago, the more massive star expanded to become a red giant, swallowing up its companion and setting in motion a process that created this butterfly effect. As the less massive companion spiraled inward towards its massive partner, rings of gas were expelled. As the hot core of the red giant was gradually exposed, powerful stellar winds inflated two huge bubbles of gas, producing the butterfly effect.

Continuing north through Monoceros, we come to NGC 2261, �Hubble's Variable Nebula�. It�s named after Edwin P. Hubble, who carried out some of the early studies on this object. The nebula is a fan-shaped cloud of gas and dust that is illuminated by R Mon, the bright star at the apex of the nebula. The variability comes from dense condensations of dust near the star casting shadows out into the nebula. As they move the illumination changes, giving rise to the variations first noted by Hubble. There is probably a symmetrical counterpart of the fan-shaped nebula on the southern side of the star, but it is heavily obscured from view by dust lying between this lobe and our line of sight.

NGC 2261 Credit: HST, NASA, JPL

The star, R Mon, can't be seen directly, but only through light scattered off of dust particles in the surrounding nebula. R Mon is believed to be a massive young star, with a mass of about 10 times the Sun, and may be only 300,000 years old. It varies irregularly from about magnitude 11- 13.2.

By this time, someone will have asked you, �Hey, what is that bright red star up there?� You can make their day as you tell them it�s the planet Mars. Unfortunately, it will have shrunken to about 10.4 arc seconds by mid-March and will be a pretty underwhelming site in most telescopes on an average night. But everyone will want to look anyway, just so they can say they saw it.

Lucky for us, about 35 arc seconds away to the southwest lies RR Cnc, a pretty interesting Mira with a range of 9.8-15. Mars never moves far from RT Cnc in March, so you can the red planet as a guidepost to one of my favorite red stars in Cnc.

Continuing east-southeast you�ll run smack into the enormous star cluster M44, the Beehive Cluster, or Praesepe (Latin for manger). This cluster is easily visible to the naked eye from suburban skies and contains several variable stars within it, including the eclipsing binary, TX Cnc and several Delta Scuti variables. But I�m going to point you to U Cnc, about 1 degree southwest of the center of the cluster. U Cnc is a Mira that varies from 8.5- 15.5. The charts and sequence have been extensively revised to cover the entire range adequately, making this star a joy to observe nowadays.

The other open cluster in Cancer is of course, M67. M67 is one of the oldest known open clusters, believed to be about 3.5 billion years old. Open clusters usually self-destruct before reaching this age. Being such a mature cluster, it has many evolved red giants within its population of 500 or so stars. To me, M67 is merely a star hop jumping off point to get to AK Cancri, a nice little cataclysmic variable in Cancer. For such a small constellation, Cancer is endowed with lots of cataclysmic variables, namely DW, AK, SY, GY, GZ, DE, CC, AT, EG, YZ, HH Cnc and SDSS0808.

AK Cnc is dangerously close to the ecliptic, so it�s not unusual to find an asteroid or two in the field when observing. You need to be sure you are actually witnessing an outburst or you may find yourself embarrassed by a pesky asteroid.

Regulus is another bright star in the spring sky, and makes a perfect place to begin your star hop to one of the all time favorite Miras in the AAVSO program, R Leo. From Regulus, alpha Leonis, you pan west to nu Leonis and then about the same distance again to 18 and 19 Leonis. R Leonis is just south of 19 Leonis. Once you�ve found the triangle of 18 and 19 Leonis and the star due east of this pair, you will never forget it. R Leo varies from 4.4 to 11.3, so it is always visible in a small telescope, and often only binoculars are needed.

Leslie Peltier recounts in �Starlight Nights� how, after several unsuccessful attempts at locating it he finally found and observed his first variable, R Leonis, on March 1, 1918.  Like many of us, after that first success, we feel foolish when we realize our own mistakes that prevented our initial success. It was the same for Peltier. He wrote, �every March first since that night, whenever the skies were clear, R Leonis and I have recalled our first meeting by making a mutual estimate of our brightness�. Even though there isn�t a deep sky wonder of any consequence nearby, I think a spring night out with the telescope warrants a visit to R Leonis. As it happens, the active cataclysmic variable, X Leonis resides just northeast of the anonymous member of the trio with 18 and 19 Leonis, making this location a frequent stop on my patrols.

10.5 degrees north of R Leo is one of the finest galaxies in the sky that is not a Messier object, NGC 2903. How Messier ended up missing this bright galaxy has got to be purely bad luck. Three of Messier�s comet discoveries came very close to this galaxy and one, the second comet of 1760 actually passed within 1.6 degrees of it on the night of march 11-12, 1760. William Herschel eventually discovered it, in November of 1784.

NGC 2903 Credit: NOAO

On and two thirds of a degrees east-southeast is AB Leo, a semiregular variable with a range of 10.7-13.2. This one is easy to find, there are plenty of stars and asterisms to help identify the field, and the current AAVSO charts cover the range nicely.

Also in Leo is M105, a bright elliptical galaxy that actually looks like a comet in the eyepiece. It is flanked closely by NGCs 3384 and 3389, forming a nice trio of deep sky delights. 1.5 degrees to the northeast is W Leo, a Mira with a period of 392 days, varying between 8.9 and 14.8. There are so many galaxies in this region of the sky you�ll be forgiven if you end up off the beaten track and miss W Leo. But she�s a fine Mira worthy of your attention once you�ve taken in an eyeful of galaxies.

Heading due east through the lion�s tail, beta Leonis, and then another 10.5 degrees, lays M88. This is an impressive spiral galaxy. The infrequently outbursting cataclysmic variable, AL Com lies in the same field of view, and is not likely to be in outburst when you visit, so go ahead and take some time to wander in the �Realm of Galaxies� here. There are a lot of Messier galaxies around here- M49, 58, 59, 60, 64, 84, 85, 86, 87, 88, 89, 91, 98, 99, 100, you get the idea. You may spend more time looking at galaxies than variables tonight, but we�ll let it go this time.

For this season�s �piesta resistance� we have a trio made in heaven. The constellation Virgo features the giant spiral galaxy M61, host of at least six supernovae, the planet Saturn with its rings opening up from edge on and the excellent Mira variable SS Virginis. Together they form a nice triangle with something to please everyone at each apex. I would start with M61, to get people looking for faint fuzziness and to sharpen their eyepiece skills, then move to the variable before ruining your night vision staring at brilliant Saturn and his impressive rings.

We�ll continue this series with the final installment in summer. Until then, happy hunting.
 

The Loneliest Guy at the Star Party

I don't go to star parties very often anymore. Packing up all the gear, telescope, food, clothes and setting off to remote dark sky sites lost its appeal to me somewhere along the way.

Star parties are part camping trip, part observing opportunity and part social event. Anywhere from a few dozen to hundreds of people come together, pitch their tents or park their campers, set up their telescopes in an open field, swap equipment and stories and share the views through their telescopes through the night.

My wife went to one star party with me a long time ago. She doesn't like to be cold, and when it's clear it's usually cold. She doesn't like to go camping much either. Forget raccoons and porta-potties. Her idea of 'roughing it' is staying in a hotel that doesn't have room service.

I tried my best to make her comfortable. We had these brand new camp lounger chairs, I tucked her into a sleeping bag in the lounger, and covered the sleeping bag with a plastic tarp to keep the dew off her and made a little hood for the back of her head. It was August, and I figured she could at least sit back and watch for Perseid meteors. After a short time, I real bright one exploded overhead and I could hear everyone around us who happened to see it oohing and aahing. Coming from Irene's lounger was the distinct, lady-like, unmistakable sound of snoring. I went back to observing variables with the telescope.

My observing program is mostly cataclysmic variables. 9 out of 10 observations I make are 'less than' observations. In other words, I don't see the star, so it's not in outburst tonight, and I record the faintest comparison star I can see in the eyepiece to set an upper limit on the star's brightness, for example <14.9. Then I move on to the next field to see if anything has popped up since the last time I visited there.

As is the custom at star parties, eventually someone comes around to see what you are looking at and asks for a peek in the eyepiece. So I give them a quick primer on cataclysmic variables, show them the chart so they can identify the field and let them have a look. They stare into the eyepiece for a minute and then say, "where is the variable star?" I tell them it's too faint to see and they walk away somewhat disappointed. Or they'll say, "I can identify the star field, but it's not there?" to which I say, "I know, isn't that cool?" As they walk away they warn the next curious spectators, "Don't go over there. He's looking at nothing!"

It takes a special kind of nutty to do what I do. Like I said, I don't go to star parties very often anymore.

Double Dipping- Autumn

Most nights, I race through my variable star observations, trying to log as many as I can get as fast as I can go, before the weather changes, I run out of steam or the Sun comes up. I hop from field to field; completely ignoring celestial wonders just a few degrees away. When the longer, clear, dry nights of autumn finally come, I am tempted to take a few extra minutes along the way to take in some sights and try new challenges.

Lets say tonight is one of those glorious clear, moonless, autumn nights. You�ve decided to stop and smell the roses along the way, but you�d still like to make some variable star estimates. Or maybe a couple friends or family have stopped by for a late dinner, and now they want to look through the telescope. You need a plan. 

Obviously, we�ll start in the west and north with targets that will begin to fade into the haze of the horizon if we don�t get them right away. Since it is still experiencing a record minimum, in magnitude and duration, I think we should be sure to observe R CrB first. This star could be considered a deep sky wonder itself. Usually visible in binoculars as an unassuming sixth magnitude star inside the �Northern Crown�, R CrB undergoes sudden, random fading episodes, sometimes to 14th magnitude. As of this writing, it is hovering just above 15th magnitude, where it has remained for longer than ever before in recorded history.  In the same low power telescopic field is the semiregular variable TT CrB, ranging from 10.9- 12.1, just north of R CrB. If you have a telescope large enough to see R CrB around 14.8, you may want to continue on from TT CrB to the bright 7th magnitude star to the NW, GCS 2039 0642. Just about 10.5 minutes north of that star is a faint, round 14th magnitude galaxy, NGC 6001. I�d put identifying this in the �challenge� category. To me it looks like a slightly fuzzy star, but hey, we�re just getting started.

Before you leave CrB be sure to at least check in your finder to be sure the recurrent nova T CrB hasn�t erupted. If it has, you�ll see a bright star forming a triangle with epsilon CrB and delta CrB. Stop everything at that point and send out an alert. Forget the faint fuzzies!

Much more impressive in a telescope is M5 in Serpentis. This is about as low as we want to go, and this is a better summer target, but the irregular variable Z Ser is only 38 arc minutes away, and this star is almost totally ignored by observers. AAVSO has very little data on it. The GCVS lists a range of 9.4-10.9, and a period of approximately 88 days, so it should be interesting and easy to follow. Why don�t you adopt this star into your program, and pick it up again in spring when it comes out of conjunction. It will give you an excuse to observe M5 on a regular basis without diminishing your serious variable stars observer status.

From there we swing north to the great globular M13 in Hercules. Even I�m not so jaded that I don�t like to take a few minutes to take in the finest globular cluster visible in the northern sky. But let�s not get carried away. Waiting for us about one and a half degrees NW is the fine Mira variable W Her. W Her varies from 8th to 14th magnitude, so it�s usually visible in an 8-inch scope, and always visible in a 10 or 12-inch.

About halfway to our next destination is an anonymous little star cluster in Lyra, easily visible in your finder scope. Just to the east of the two brightest stars in the cluster is CY Lyrae, a fun little U Gem star that is fairly active, outbursting into the 13th magnitude range every couple weeks or so. Even if it�s not visible tonight, you won�t have wasted your time visiting here. This one is off the well-beaten path of deep sky wonders. It�s a pretty well kept secret amongst variable star folk, and we aim to keep it that way, so shhhh�don�t tell anyone. 

If you have company at the observatory, M57 is one of the stops you�ll make anyway, so here is your chance to quickly locate and show them a real crowd pleaser, the Ring Nebula in Lyra. Located in the same low power view as the ghostly ring of this planetary nebula is another Mira variable RX Lyr. If you make it a point to observe this variable this month you�ll be able to make a positive observation as it is just beginning to fade from maximum, around 11.2, on its way to the inner sanctum. It spends a lot of time fainter than 14th magnitude, so I always consider it a treat to make a positive observation of a variable so close to M57.

Our next stop is in Draco, the Cat�s Eye Nebula. Located about midway between zeta and delta Draconis, this is another bright planetary nebula on the usual star party agenda. Yes, it�s nice. Take a few moments to soak it in and explain to your guests how planetary nebulae are the remnants of old evolved stars, and then swing about one degree SE and you can show them two such stars in one field, W and X Draconis, one of my favorite �twofers� in the sky. X Dra is located next to an unmistakable triangle of field stars and should just be visible in a 10 or 12-inch around 14th magnitude if you hurry. Like RX Lyr, it spends a good deal of time fainter than 14th magnitude and has a period of 257 days. W Dra ranges from 9-15th magnitude, so it is almost always visible in medium sized scopes. These two are only 14 arc seconds apart, so they are in the same medium to high power field.

From there you can glide into the Milky Way, starting your tour with everyone�s favorite double star, Alberio, beta Cygni. Beta 1 Cyg, the orangish K star of the pair is even suspected of being variable, although I doubt you could do much to prove or disprove this visually. But it is one of those fun facts I like to throw in just to discourage guests from ever coming to a star party at my observatory again! From there it is a relatively easy jump to M56, a globular with a bright core, about 3.75 degrees NW of Alberio, and then almost due east 4.7 degrees is one of the prettiest star fields containing a variable star in the sky. The variable is EM Cyg, a Z Cam star that varies from 11.9 to 14.4, so it is always visible in medium sized telescopes. After you�ve made your estimate you can encourage visitors to slowly slew around the area getting lost in the diamond-clustered field against an ink-black backdrop.

Continuing along the body of  �The Swan� to the NE you�ll come to chi Cygni. With a dramatic range from naked eye visibility (magnitude 3 or 4) to 14th magnitude, this is one of the AAVSO �legacy Miras�; with data going back a hundred years or more. If tat isn�t enough to impress visitors you can track down any number of star clusters, planetary nebulae or diffuse nebulae within a couple degrees of this variable. In fact the area east of chi is a large bright diffuse nebula with the sexy name GN 19.50.2. If that doesn�t impress your guests, slew NW to the �Blinking Nebula� and demonstrate averted vision with the �now you see it, now you don�t� planetary nebulae NGC 6826.

You�ll have to go south again to visit the Dumbbell Nebula, M27. Then you can take a break from the telescope to observe one of the stars in the 10-Star Training Tutorial, eta Aquilae. This is a bright Cepheid observable with binoculars or the naked eye. The observant visitors will want to know what that bright star is in the south, so be prepared to blow your dark adaptation with some glaring views of Jupiter and the Galilean satellites.

By now M31 should be high enough to see with the naked eye from a dark site. You can show visitors where you�re pointing the telescope next while you explain that the Andromeda Galaxy is the furthest thing you can see with the naked eye, some 2.5 million light years away. After you get an eyeful of Andromeda you can swing over to another AAVSO favorite, RX And. This active Z Cam star ranges from 10.3 to 14.0 and it is always doing something. It�s either trying to hide around 14th magnitude, in outburst at 10 or 11 or stuck in a standstill somewhere in-between on any given night.

A little further east and you�ll come to U And, a nice well behaved Mira that varies from 9.9 to 14.4 in 346 days. It�s in a very nice field of stars with a bright triangle of 8th, 9th and 10th magnitude stars to the NE of the variable.

This is a good point to stop. If you really want to squeeze in one more deep sky treat you can slew south to M33 before capping the telescope and calling it a night. Depending on how late it is in the evening or the season, hints of the winter sights to come may be just visible in the east as Orion begins to rise into view. In the next issue, we�ll talk about deep sky treats and variables worth braving the arctic air of a northern winter.