Haverford Astronomy department blog
A few weeks ago, Scott Engle (visiting instructor) and I spent some quality time with Haverford’s 16-inch telescope. One of Scott’s hobbies is photography, so he brought his digital SLR camera along and hooked it up to our telescope. Here are a couple of things the beautiful things that we saw, Jupiter and three of its moons and our own Moon:
Wow, Tonima said pretty much everything about our part of the trip! I guess that leaves me to show you how it went.
Picture # / Description:
1) Scott and Tonima, well rested and ready to head up the mountain!
2) Welcome to Kitt Peak!
3) Can you guess why it might be a problem to drive on a curvy mountain road without headlights (so as to not disturb image taking)?
4) Land of Domes! Taken from our ridge, looking onto the next ridge.
5) The WIYN 0.9m Telescope! Notice the louvers to help control the conditions inside the dome.
6) The McMath Solar Observatory. What you see is in fact only 40% of the telescope, the rest is underground!
7) They’re not kidding. The group who was observing the night we arrived, John and Scott from Indiana University in Bloomington, IN showed us a video of them attempting to drown a scorpion back down the drain. Needless to say, we kept those drain covers particularly tight and checked our shoes before putting them on each morning.
8) Looking out towards the Mexico border, only 60 miles away.
9) The telescope. Big enough that Tonima needed a bit of help to get the mirror cover off, even standing on the ladder.
10) The Steward Observatory, operated by Arizona University. The most recognizable object on the mountain.
11) The VLBA radio telescope on Kitt Peak. This telescope works in parallel with 9 other arrays across the country, from Hawaii to Connecticut to the Virgin Islands, forming an effective array size of 5000 miles!
12) More friends that lived at the house.
13) The sun arises after a long night of observing, as we drive back to Tucson.
The disk of the Milky Way was visible as a dense, thick disk of stars across the sky. Once Orion nebula rose, we saw the super-red Betelgeuse and whiter Rigel. Andrew and I even spotted a shooting meteor, which Scott missed because at that instant he was unfortunately looking through a pair of binoculars.
Hello, I am Tonima Tasnim Ananna, a sophomore from Bryn Mawr College, a declared Physics major (at Bryn Mawr), undeclared Astronomy major (at Haverford), and one of the members of the recent ASTR341 Observational Astronomy group which went to Kitt Peak National Observatory (KPNO) at Arizona to find some RR Lyrae stars in faint satellite galaxies of the Milky Way. I’m so appreciative that the Louis Green Fund was available to support this trip to an observatory.
The satellites that we observed are galaxies Segue 2 and Segue 3, and Ursa Major 2 as control. The telescope that we used at KPNO is a 36’’ telescope called WIYN 0.9m.
Before we start, I will give a little bit of background on RR Lyrae star. These starts are special because they are a type of Pulsating Variable star – a kind of stars which periodically change their radius and luminosity, and reside in the “instability strip” of a HR-Diagram. The pulsating variables have a shell with temperature around 40,000K – a temperature at which Helium is ionize from He+ to He++ – very close to its surface. This releases a lot of electrons into the shell, and as electrons scatter photons, this shell is very opaque to photons. The photons which random walk out of the hot core of the star cannot pass through this shell, and hence create a lot of pressure on the shell’s inner surface, forcing it to expand. As the hot gas expands, its temperature drops, and much like the surface of last scattering of the early Universe, the helium neutralizes and the shell’s opacity drops, and the photon flies free, suddenly increasing the luminosity of the star. But there is more to these stars than the cool Physics, these stars play a very useful part in gauging astronomical distances: their luminosity and period are related, so if we can find the period of such a star, we can find its absolute magnitude, and using the distance modulus, we can thus find its distance from us. This makes them excellent standard candles, and gives us the motivation to try to find them in faint galaxies like Segue 2 and 3, which have not yet been studied extensively for RR Lyrae.
To prepare for the observing run, at first we studied a handful of faint satellites of the Milky Way, prepared their hourly airmass table for the approximate time of our observation, and it turned out that the Segues make excellent objects for observation, with airmass smaller than 2 most of the time throughout the period of our observation. We approximated the expected background count based on lunar age at the time of our observation (around 7 days), and calculated exposure time that would give us a satisfactory signal to noise (100). The plan was to take images of the galaxies over a few hours (the RR Lyrae have periods of around half a day), and study the images for any changes in luminosity of stars over the period of observation. We used three different filters (B, V and I) to take the images.
The class split into three teams, and our team consisted of Assistant Professor Scott Engle, Andrew Sturner, and me. We were the earliest team there, and we observed the night of October 13th, 2010. We arrived at Tucson on the night of 10th, stayed at a Hyatt place for the night, went shopping for groceries the next day, had lunch at a restaurant called “Brushfire” which had excellent food and pictures of hell on its wall (to symbolize their food is spicy perhaps). Then we headed towards KPNO to observe. Tucson is surrounded by mountains, which was a treat for me because my native land, Bangladesh, is extremely two-dimensional. KPNO itself is on top of a mountain, elevated 7000ft above sea level, which, we found out, affords it exceptionally dark skies, far from city lights. We were inaugurated to our telescope’s system by another team working there on the night of the 12th. During the training, we had time to wander outside at the sight, and take in the amazing night sky above the mountain. The disk of the Milky Way was visible as a dense, thick disk of stars across the sky. Once Orion nebula rose, we saw the super-red Betelgeuse and whiter Rigel. Andrew and I even spotted a shooting meteor, which Scott missed because at that instant he was unfortunately looking through a pair of binoculars.
Prior to the KPNO trip, most of our experience with telescopes was limited to the 12 and 16’’ Cassegrain telescopes at Haverford. This semester, we also started using CCD cameras to take pictures of our objects of interest. The telescope which we used at KPNO was 36’’, and with all due respect to our beloved 16’’ telescope, the WIYN 0.9m had a much more sophisticated system, complete with a liquid Nitrogen Dewar to keep the pixels of the CCD camera (called S2KB) cool to avoid thermal electron emission, and a system to take “dome flats”, or images of a flat field to correct our object images for biases in the camera’s pixels’ outputs. Another notable difference between the WIYN telescope and the 16’’ was the use of the Guide cameras – the WIYN telescope uses two special guide cameras to keep track of a star, and constantly outputs the degree to which the star’s image deviates from its centre, to verify that the telescope is keeping track of the our object of interest. But the best part of all has to be how little time we actually spent in the dome: we only needed to go to the dome to take a peek to verify everything looks as it should, and to fill the liquid Nitrogen Dewar. This was very comforting for me because last year when we were working for hours in the dome with the 12’’ telescope, no matter how much clothes I wore I always seemed to under dress by two jackets, and am sure was losing enough heat to be luminous myself. (But it was still fun when we got to look at the craters of the moon, and blue-green Neptune and Uranus).
On the 12th, we woke up late because we have to stay awake throughout the coming night, had some food and went to meet Hillary, the sight supervisor, who gave us a second overview of the system. We filled the Dewar with liquid Nitrogen, and left to drive around the observatory. We were back a couple of hours later (around 4:30 pm) to take dome flats. We opened up the dome vents, turned on the exhaust fans and the dome flat lights (low intensity for our filters). We took 5 dome flats in each filter, 10 bias images (bias accounts for spontaneous reading by the camera for 0 second exposures), and by the time we were done with these, the sun has set, and it was time to start the Guider cameras to track a star. We looked through both guide cameras, and found an auspicious looking star (sorry about the bad pun) in the north camera. We started tracking it using a computer called MOSS, and entered the RA and DEC of Segue 3 in another computer called Olive. We moved the telescope to Segue 3, and using the focusing system of the computer Emerald, we analyzed a series of seven exposures of the galaxy for different focus values, and decided on the best focus value (in units particular to the system) for our images. The focus value changes with temperature, so we kept monitoring the temperature of the dome to see if we needed to make any adjustments. Luckily for us, temperature remained stable inside the dome and we only focused once per object. We started taking exposures (around 7 pm), and Professor Willman and her teams arrived. They were studying our activity the way we studied the other team the night before. We refilled the Dewar in the middle of observing Segue 3, because it needs refilling every 8 hours, and to show the other team how to do so. Then they left to rest, and we continued taking exposures of Segue 3, and completed 13 sets by midnight. Then we worked on a synoptic project which requested us to take pictures of M31 – Andromeda – in R band. We spent around one and a half hour taking flats, biases and images for this program, emailed them a notification, and moved to Segue 2. We refocused, took images of Segue 2 for a few hours – this time only in B and V band. We only managed to take 9 sets for Segue 2, and then had to move to Ursa Major 2. We took around 5 images of UM2 in V band, and then it was time for us to leave to catch an early flight back to Philly. We refilled the Dewar, and left pretty energized, even though we were up all night!
Now that we are back from the trip, we plan to analyze the images we took for a lab for ASTR341, and spot (fingers crossed) some standard stars that would help us estimate the distance to Segue 2 and 3. It is fun to solve problem sets, but it is much more satisfying to do something hands-on that produces a meaningful result, like this project. Even if we don’t get the result we are expecting, we still developed a better idea how real observers observe, and I personally got to observe the disk of Milky Way with naked eyes!
The five best things that happened to me and Emily Cunningham during our 12 am – 6 am shift at the 0.9m telescope at Kitt Peak National Observatory last night:
5. Mastering the art of filling the dewar with liquid nitrogen.
4. Overcoming a myriad of technical issues, including the fact that the telescope would not move at 6 am.
3. Not falling asleep.
2. Managing to obtain several good images of Segue II, a candidate dwarf galaxy, for science!
1. Taking exposures of the Trapezium Cluster in the Orion Nebula in four different filters. We hope to combine these to make a beautiful picture when we get back to Haverford!
Better than all of these things: not finding scorpions or snakes in our beds!
Greetings from the 0.9m telescope at Kitt Peak National Observatory! I’m here with Annie Preston, Emily Cunningham, Tim Douglas, and Erin Boettcher (Tonima Tasnim Ananna and Andrew Sturner were here, but already went home). The generosity of the Louis Green Fund supported all of the students to travel here to obtain observations of some Milky Way companions. The students will be posting here about their experiences, but limited internet access and long working hours are delaying our posts.
In the meantime, click for: a flavor of what we do all night long.
Last week, I took my Astronomical Ideas class to Haverford’s Special Collections wing in Magill Library to discuss and interact with our first edition of Copernicus’s 1543 de Revolutionibus (On the Revolution [of the Heavenly Spheres]) and our first edition of Newton’s 1687 Principia. Ann Upton of our Special Collections department generously arranged a session with these books for my class. She also brought Owen Gingerich’s amazing book describing his census and study of all first and second editions of the Copernicus book, and a transfer of debt that had been signed by Newton. Fewer than 500 copies of the Copernicus book were produced in the first edition, and only 300-400 copies of the Principia were produced in its first edition. So these are two rare commodities.
Here, you can see Ann showing students the Gingerich book, in which he presents i) the results of his study of the marginalia of the hundreds of Copernicus books he inspected, in an effort to learn about the impact of Copernicus’s work on the evolution of astronomical thought and ii) the present locations of all books he inspected, their individual histories, and individual interesting facts:
Gingerich’s census revealed many juicy tidbits about the influence of Copernicus. Gingerich’s census was inspired by a richly annotated version of the book he viewed in the Royal Observatory in Edinburgh (if my memory serves me correctly) that had been owned by one of the leading astronomers of the 16th century. The detailed annotations made no mention of the heliocentric model that Copernicus is famous for today. I was particularly fascinated by the marginalia that Gingerich found in the copy that has been owned by Kepler, but previously owned by someone else. Gingerich found that two passages in particular had been annotated prior to Kepler acquiring the volume: One notation was of a passage where Copernicus raised the question of whether the center of the Sun or the center of the Earth’s orbit was the center of the Universe. Another notation was the word “ellipse”(!) written next to a passage where Copernicus was discussing the shapes of planetary orbits that included epicycles.
In this shot, you can appreciate the beautiful table with a wood base and glass top that the books were presented on. The Principia is on the left and De Revolutionibus is on the right, with Newton’s picture in the middle. Its amazing that any student can thumb through these works:
Finally, here is a cool candid of students using a flashlight on the Principia to detect the presence of the chain lines going crosswise through the pages. Chain lines – light lines hidden in the paper – are an artifact of the way paper was made back in the times of Copernicus and Newton. The crosswise orientation of the chain lies here reveals that this book’s pages were printed as “quartos”:
