Week 1: Across the sky, half a degree at a time

Once I blazed across the sky,

Leaving trails of flame;

I fell to earth, and here I lie –

Who’ll help me up again?

A Shooting Star, Johann Wolfgang von Goethe

Orion was always the easiest constellation for me to pick out; up in the winter, where the clouds in the Pacific Northwest might clear for a few days at a time, beaten back by the frigid wind, the hunter’s belt shone bright enough to cut through the pollution of southeast Portland. Atop Kitt Peak, the hunter was lost amidst thousands of stars that pincushioned the night. On our second night, when we took a break to stargaze near midnight, I saw my first shooting star. Then, as if to unite us in awe, the brightest streak of light arced towards the western horizon. You could almost feel my second shooting star pass by.

I thought observing would be much more complicated, stressful, and fast paced then it ended up being. After a long day of travel and what felt like a longer first night on the mountain, I got settled into something of a routine: wake at 1pm, relax until 3:30pm, walk to the telescope to take calibration images, get dinner and pick up night lunch at 4:30pm, and then open the dome and begin the night of observing (sometimes with twilight flats).

Work during observing was spread among four stations: Operating the camera and taking images (yellow shirt), driving the telescope and keeping physical logs (blue shirt), operating the guide camera and keeping digital logs (blue shirt), and keeping the narrative log (red shirt). With five students, this meant in a given rotation one person would be on a break (red shirt). After taking a set of data on a given target-field, we would rotate positions.

The Half Degree Imager (HDI) camera is a CCD that currently services the WIYN 0.9m. It returned from repairs just in time for us to use it for our data collection. The camera hosts 4096 x 4112 pixels, each with a physical size of 15 x 15 microns. The pixel scale is 0.43 arcsec, so the camera has a FOV of 29.2 arcmin (60 arcmin = 1 degree, so ~30 arcmin = 1/2 degree). Unfortunately for us, we could only run the camera in its 1 amp, 38s readout mode (as opposed to a faster 4 amp, 9 sec readout), but the camera has some really cool properties despite its lengthy readout.

The telescope is cooled to about -105 ºC and incurs only about 5 electrons per pixel per hour in thermal current, meaning there’s no reason for us to take dark calibration images. The telescope focus does require a bit of elbow grease, as you have to ‘jog’ the focus in order to construct a curve whose minimum is then used as the BVRI base focus, with narrowband images having constant offsets.

We took data in five filters; three broadband (VRI) and two narrowband (H-alpha and H-alpha continuum). These filters were chosen because the objects we are interested in as a class (broadly) are low mass and young; low mass stars will be brighter in red wavelengths (hence the preference for R and I band magnitudes, as opposed to U or B) and brown dwarfs and young stars will be active, thereby emitting at H-alpha as they excite hydrogen gas. By taking images in H-alpha an a filter close to H-alpha we will be able to notice the differences in certain objects that are active (because they will shine more brightly in the H-alpha images than the continuum) versus inactive stars (which will shine at effectively the same brightness in both filters).

I was assigned to a group with Lena, and we will be monitoring H-alpha variability in the Taurus star forming region, centered around the HL-Tau system (the host of a famous circumstellar disk), as well as in the TESS BD 21 field which captures 6 field brown dwarfs. There are lots of paths the science of our project could take, depending on what results we find from our initial light curves and periodigrams, but in general we will rely on I-band and our narrowband images to investigate the rotation rates and accretion/activity of our objects of interest. In particular I am very excited to stack previous epochs of H-alpha observations with ours, which will likely result in the resolution of jets and outflows from some of the protostellar Herbig-Haro objects in the HL-Tau field.

In order to reduce the data we took, we will need to re-purpose our code from last semester and likely optimize it for reducing such large datasets. My hope is to integrate some numba package optimization into an outline jupyter notebook after cleaning the unnecessary code and improving the path dependency of my previous functions. We can then push our data through bias subtraction and flatfielding and decide as a group how to stack our frames (median over each night of observation, each dataset, or the whole week, etc).

Required files

Night 1: #1-13 (Bias, header shows wrong etime), #15-30, except 28 (VRI dome flats), #32-37 (narrow flats), #52-54; 56-59 (HL Tau 1, no NB: out of focus), #95-113 (HL Tau 2)

Night 2: #235-245 (Bias), #246-250; 252-255; 2-5; 7-15 (Dome flats), #40-42; 44-58 (HL Tau 1), #83-106 (HL Tau 2, R band dim), #134-136 (HL Tau R band follow up)

Night 5: #7-17 (Bias, Jan 21st), #2-6 (V flat, Jan 21st), #2-11; 18-30 (RI, narrowband flat, Jan 22nd), #53-71 (HL Tau 1), #94-112 (HL Tau 2), #160-171 (Tess 21 BD1 1, note only RI+nb), #230-238; 240-242 (Tess 21 BD1 2, tracking failure on image 239)

Night 6: #1-11 (Bias), #277-301 (dome flats), #12-17 (H-alpha twilight flats), #51-69 (HL Tau 1, V unguided), #93-111 (HL Tau 2, unguided), #121-149 (HL Tau 3), #190-201 (Tess 21 BD1 1), #223-234 (Tess 21 BD1 2), #259-276 (Tess 21 BD1 2, 256-261 have wrong object label)

Night 7: #319-329 (Bias, Jan 23rd), #302-318; 1-10 (dome flats, Jan 23rd -> Jan 24th), #28-46 (HL Tau 1), #68-69; 71-73; 75-88 (HL Tau 2, 70&74 streaking), #109-116; 122-131 (HL Tau 3), #153-164 (Tess 21 BD1 1), #186-197 (Tess 21 BD1 2), #219-242 (Tess 21 BD1 3, 4)

Night 8: #261-275 (Bias, Jan 24th), #244-260; #1-7 (dome flats, Jan 24th -> Jan 25th), #8-25; 28-35 (Twilight flats), #51-58; 60-66; 69-71 (HL Tau 1), #94-107; 109-111; 113-114 (HL Tau 2), #134-152 (HL Tau 3), #197-208 (Tess 21 BD1 1), #230-241 (Tess 21 BD1 2), #263-274 (Tess 21 BD1 3)