AAVSO - YSO Section

  I'll catch up and post some observations I made last week soon. The big news today is that the AAVSO's YSO section is up and running, and looks great! Mike Poxon emailed the link to me today. It has tons of centralized information and charts about these fascinating, active, and under-observed stars! Here's the link:

  http://www.starman.co.uk/ysosection/

YSO's (Young Stellar Objects)

  In my posts I often refer to "YSO stars" so I thought it might be good to give a little background information about them. 

  YSO stands for "Young Stellar Object." The long-standing theory is that these are stars that are still condensing from dust and gas, and by astronomical standards they are very young; on the order of just millions of years old instead of billions of years old like our Sun. Classifying them is difficult because they come in all sizes and types. The one thing they have in common is that they usually show a lot of unpredictable brightness changes, for a lot of different reasons. Since these stars are surrounded by gas and dust, they often fade quickly in brightness and recover because the ring of dust is "clumpy" and a thick patch of dust orbiting the star might float in between our line of sight and the star. Also, if a lot of gas and dust falls into the star, this can make it suddenly get brighter as the new material ignites on the surface.

  I've looked at a couple of YSO stars for years. Just after high school, one of the stars I used to report to the AAVSO (American Association of Variable Star Observers) was called T Tauri. I also made estimates for some of the interesting stars buried in the glow of the Orion Nebula. But most of the variable stars I observed and reported to the AAVSO were long-term variables like Mira stars and Semi-Regulars. I still observe these, but my interest focused on YSO observing about a year ago. For the last decade, there have been several automatic sky surveys created. These are robotic telescopes that image huge chunks of the sky every few days and automatically record star brightness. Though the all-sky automatic surveys are a boon for science, I was starting to get the feeling that observing long-period variable stars by eye was getting obsolete because of them. I wanted to start an observing program where I could still provide valuable data. 

  In the spring of 2010, I started to realize that YSO stars weren't being studied by very many people, and that they showed brightness changes that were so fast that a lot of the automatic sky surveys missed them. I started emailing around asking if anyone observed them regularly, and this was how I struck up a pen-pal relationship via email with Mike Poxon from Norwich, England. Mike had been observing these kinds of stars for years and confirmed my suspicions; that few amateur astronomers looked at them regularly, that they were getting increasing attention from professional astronomers, and that they showed a lot of wild short-term dimming and "flickering" that was too fast for the automated surveys to catch! Mike kindly provided me with lists of Young Stellar Object targets in range of my telescope and also with charts that showed these variables and comparison stars to estimate their brightness by. He continues to serve as my unofficial "mentor" when it comes to gathering data about these stars and provides prompt answers to my stupid questions about observing them. For this I am eternally grateful! 

  Recently, Mike Poxon emailed me to let me know that the AAVSO was going to start a YSO section and forum on their website, and that he would be hosting it. I hope to be able to help him spread interest about these under-studied variable stars, and also hope to keep adding more of them to my list and making a real contribution of data about their behavior.

 

PM Fri. June 3 - AM Sat. June 4 Observing

  This night was about as hazy as it could get and still be good enough to try to get some observing done. 

  At sunset skies were white with haze or very thin high clouds. The slim Waxing Crescent Moon (2.2 days since New Moon) was faint and ruddy looking low in the West-Northwest sky at dusk. I kept checking the sky until midnight, when it looked like there was finally some improvement, and I was outside with the telescope from about 1:00 AM until a little past 2:00 AM. It was mild with temperatures in the low 70's F. The humidity was about 65%. Winds were light. The sky stayed very murky the whole time I was out there. At best the limiting magnitude overhead to the naked eye was about 4.0 but it was usually closer to 3.5. 

  With the lousy sky transparency, I decided to just follow up on some of the variables I saw five nights ago, and looked at one variable that I hadn't been able to estimate on the morning of May 30th. Here's what was done tonight:

  At 1:07 AM (5:07 UT June 4) I looked at the area of UZ Bootis, and had to settle for an estimate of <13.2 magnitude. The 13.2 comparison star could be glimpsed often but there was no sign of a rare flare-up in brightness from this star. (There hasn't been one recorded since 2003.)

  At 1:19 AM (5:19 UT June 4) I looked for T Bootis, and saw nothing at the location of this nova from 151 years ago. I recorded it as <12.5 magnitude since the 12.5 star on the chart was the dimmest I could see.

  At 1:26 AM (5:26 UT June 4) I estimated T Coronae Borealis at 10.3 magnitude.

  At 1:42 AM (5:42 UT June 4) I estimated "Skiff's Star" (VSX J182726.0-043447) as 11.2 magnitude. This was my second estimate of this star, which was found to be variable only two years ago. I'm still the only observer in the AAVSO who seems to be looking at it since discovery! I used the comparison star sequence and chart that was emailed to me by Mike Poxon in the UK.

  At 2:02 AM (6:02 UT June 4) I estimated WW Vulpeculae at 10.6 magnitude. If my brightness estimates have been accurate, this star has brightened up slightly in the last five nights.

  Indianapolis is caught between wavering warm fronts and cold fronts as this month begins. It would be nice to see a nice cool high pressure system move in and stay! This mid-summer-like weather in June has led to some awful hazy and murky observing conditions so far.

 

PM Wed. June 1 - AM Thu. June 2 Cirrus Blow-off

  A weak cold front passed through Indiana early Wednesday morning and we were under the influence of high pressure that had lowered the heat and humidity. Skies started out very sunny on Wednesday. Forecasts for the night ahead made me think that I was going to have one of those "pristine" nights with great sky transparency and no dew issues. Unfortunately, skies were overcast with high clouds by Wednesday evening and conditions were fair to poor overnight.

  The reason for the unexpected cloudiness was a common spring and summer phenomenon called (probably informally) cirrus blow-off. When a region has humid, warm, and unstable air, thunderstorms often appear as the air warms and rises. If these storm clouds reach high enough into the atmosphere the ice-crystal cirrus clouds that form at the highest altitudes can spread hundreds of miles ahead of the storm centers. On Wednesday a mesoscale convective complex set up in Kansas, Nebraska, Western Missouri, and Western Iowa. These storms were vigorous and long-lasting enough to send cirrus clouds into Illinois and Indiana. So, even though my area was under stable high pressure, we still had the blown-off high clouds from two or three states away!

  I read once that narrowing down where summer thunderstorms will appear is incredibly difficult to do. One meteorologist compared it to trying to predict where bubbles will pop up when water is starting to boil! That means that predicting which clear nights will be ruined by cirrus blow-off from thunderstorms is also nearly impossible.

New Moon June 1st

  Since that observing session before dawn on May 30th we've had some good observing weather. 

  It was mostly clear but a little hazy on the night of May 30th - May 31st. I had to be up early on May 31st so I did no observing. 

  By the evening of May 31st we had some high cloud overcast due to a weak cold front moving through the area, and these clouds persisted through the evening of May 31st - June 1st. 

  Now on the morning of June 1st skies are very clear and sunny, and the cold front is supposed to have taken away some of the high heat and humidity we've been experiencing. I think tonight will feature some great observing conditions before the weak cold front is supposed to back up as a warm front on Thursday the 2nd. 

   New Moon takes place at 21:03 June 1st (5:03 PM June 1st our time) so there will be no moonlight interference tonight.