Observing at DCT

This page gives a general overview for visitors and staff

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Updates (and Old Updates)

The DCT closed up early on Friday night (12 January) and will not be operating tonight (Saturday), and most likely not Sunday night either. I would put Monday in the possibly column.

The issue in question is that some of the bolts that hold the dome track to the main ring beam have broken. The track is the bearing surface that rides on the bogeys as the dome rotates. There are several hundred 3/4inch diameter bolts that hold the dome ring beam to the track, and the rest of the dome rides on that. Two bolts were found broken during the day Friday. The pieces were removed, the shims replaced and new bolts inserted. Unfortunately, another bolt was found broken that evening, and a fourth bolt was found Saturday morning. We decided to cease any dome movement until all the bolts and associated shim can be inspected, and any that are found damaged be replaced.

Bill, Frank and Ben are in the process of removing, cleaning, inspecting and replacing the bolts that hold the dome track to the ring beam. Ben has procured 280 new bolts out of a maximum possible need of 394 (if we have to replace all the bolts). As of 4pm MST Saturday, when I talked to Bill, there were a total of 4 broken bolts (3 from Friday, 1 found Saturday morning), and they had pulled and replaced another 25. The shanks of two of the broken bolts are frozen in the holes and will need to be extracted, and the holes re-tapped. The bottom line is that this is a time consuming and tedious process, but essential.

At this point, we do not know what has caused the bolts to fail. Presumably after the bolts have been replaced we will have more information, and maybe a better idea about what happened.

LMI was pumped on Monday, January 08th, 2018. It began cooling again before 4:30pm MST. Initial reports are that things went smoothly. It will be ready for Tuesday. Any ToO's triggered on Monday night might find LMI cold enough to be usable. Check with the TOs for the temperature.

As planned in the DCT 2018A schedule release email, On 2018Jan03, we removed the DeVeny spectrograph from operations for the next several weeks to work on the detector pattern noise issue. No programs requesting DeVeny were scheduled during January, so this will primarily impact ToO programs. The exact return dates will depend upon how the work goes. This note will be updated as we know more.

DCT 2018A Schedule released (2017Dec06)

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.