Observing at DCT

This page gives a general overview for visitors and staff

(Please send us any comments or suggestions for ways to improve these pages.)

Updates (and Old Updates)

DCT 2018B Call for Proposals released (2018Apr10)

We have been advised that the USFS is planning a controlled burn this week, now scheduled for Wednesday through Friday. Depending on the weather, they are planning to burn up to 1000 acres per day. Lonnger term, they are expecting to burn 8000 acres over the next several weeks. The location for this first burn is almost due south of DCT, and may impact operations at the telescope.

The work on the DeVeny CCD camera noise has been completed, and the DeVeny is once again in operation. Many thanks to Tom Bida for the hard work on what has been a persistent intermittent problem. In Tom's words: "The baneful and puckish pattern noise of image readouts past has been largely squelched, through isolation of all ground and shield lines that pass through the hermetic connector."

The improvement may be seen in the attached 4 panel image that Tom provided, along with his caption.

Lower left: beat pattern of pickup noise before modifications, sigma=3.07 DN (4.65 e- noise). The peak-to-peak amplitude of this pattern example is about 4.5 DN.
Upper left: bias frame in lab following mods, sigma=2.75 DN (4.15 e-)
Upper right: unshuttered out of focus pinhole image in lab (the greyscale bar comes from this image)
Lower right: bias frame on DCT post-mods, sigma=2.73 DN (4.12 e-)

Gain and readout noise were measured in the lab with the current controlled source, at 1.5 e-/DN and 4.0 e-. According to the detector data sheet, this noise level is close to what is expected at our CCD clocking rate.

A very low level partial noise pattern has been observed in a few bias frames on the DCT, so we will keep an eye out for those. Bias images taken on the DCT also appear a little more mottled and streaked (for lack of better words) than in the lab, but this doesn't affect the stddev's. Also, noise was seen to increase about 0.1-0.2 counts in biases taken while DeVeny motors were in motion. Hopefully the overall noise performance won't change during on-sky operations.

The LMI User Manual has been updated. The new version is dated 2017 October 27.

From Phil: "There have been some minor updates to the LMI manual: (a) revision of starting focus value, (b) addition of filter curves for the WR filters (thanks, Amanda, for the reminder!), and (c) reorganized where some of the data files (filter curves, etc) are kept on the web and changed the links.

As always, the manual may be found at: http://www2.lowell.edu/users/massey/LMIdoc.pdf"

2017 Sept 21: Because of the differences in the re-installation of the secondary mirror, there are two key items that impact observing:

The nominal focus offsets for each instrument have changed, some of them significantly. Please, please, check with your TOs for current nominal focus offsets before setting them yourself, at least until you are comfortable with the current range of settings.
The actual performance of the optics has changed. The predictive model that keeps the optics tuned is in the process of being re-built, but will take some time. In general,
1. If you have had the optics tuned up recently, near where you are observing, things should be ok.
2. If you have not tuned recently, or have slewed a significant distance, or the temperature has changed drastically (by more than 5 degrees C or so), then you should ask the TO to re-tune.
3. If you think your focus needs to be checked, then you should consider asking the TO to re-tune the optics.
4. In particular, we are recommending that on split nights, the optics be tuned at minimum at the night start, and at turn over in the middle of the night.

2017 Oct 10: Change to all focus offsets:

In addition to the changes, as of 10 October 2017, we are moving the primary down, which will change the M2 focus offsets by a roughly constant value. This is necessary because of the limitations in M2 piston in extension. Without the shift to M1, we will not be able to focus DeVeny and NIHTS as it gets colder. The M1 offset will reduce the M2 offsets by roughly 1000microns. Again, check with your TOs for the latest values.

As part of an effort to address safe access to the DCT, we have added an alarm keypad by the backdoor of the telescope building. This means that you can enter through either the normal front door, or if the steps are icy, you can enter through the backdoor. We are also in the process of installing an overhead shield above the backdoor to protect against snow and ice falling off of the dome.

The same alarm code that works for the front door will work for the back one.

2017 Sep 21 - The DeVeny Spectrograph Manual has been updated. The new version is v. 170921.

One item in the new manual that has changed from what was in earlier versions of the manual is in the step where you log into vishnu to start up the slit viewing camera (manual version 170420, page 22). The ssh command should be changed slightly to:

    ssh -Y lois@vishnu

The -Y replaces the -X that is listed.

For LMI, DeVeny, and NIHTS, the primary User Interface machine has shifted to dct-obs1.lowell.edu. This is instead of baggins.lowell.edu. The user name and password for dct-obs1 are different from those on baggins. See your TO when you are on-site for this information. If you will be observing remotely, please contact either your TO or Stephen Levine (sel .at. lowell) to get the updated credentials. Observing should otherwise look pretty much the same as before. If you notice a problem, please let us know.

The LMI VR filter has been moved from the upper filter wheel to the lower wheel.

In late August 2017, I took a quick look at the VR filter dome flats in the upper and lower wheels. The letter-boxing effect is less pronounced when it is mounted in the lower wheel (images and normalized row plots attached - the plots have been shifted to separate them on the plot). In the row plots, the upper wheel shows about 2.5 to 3% peak to valley variation, and the lower show about 1 to 1.5% on the rows through chip center. They are worse towards the corners. I have moved it to the lower wheel.

VR should be added to the list of filters used in the lower wheel only.

The VR filter was used mostly in the upper wheel prior to Summer 2017, though it was not mounted there exclusively.