HUT Frequently Asked Questions

The Mission

1) What is HUT and What Does it Do?

See the HUT project answer.

2) What is the history behind HUT?

See the HUT history page.

3) Where can I find a HUT Technical Summary?

See the HUT technical summary page.
A detailed view of the HUT2 telescope module can be seen in the hardware chapter of the HUT data handbook. or alternatively in the HUT instrument and operations page.

4) What are some major publications using HUT data?

See the HUT publications page.
Note also the papers by Kruk et al. on final calibration of HUT 1 and HUT-2 (ApJS, 122, 299) data.

Data Handling

5) How do I retrieve HUT data?

Data retrieval proceeds in much the same way as most other MAST-archived datasets. Go to the how to search HUT data page for instructions and the HUT search page for downloading of data. Data will be returned very quickly in a tarred file consisting of many zipped data files and an ASCII filetypes.txt file explaining some of the contents. For further information go to the HUT data products page.

6) How do I read HUT data?

See the HUT data reading page.

Data Characteristics

7) What are the instrumental error sources in HUT data?

Unwanted time-dependent signals (dead time, phosphor persistence).
Airglow in emission lines (geocoronal Lyman alpha can be the dominant feature in the spectrum).
Extreme UV contamination (white dwarf only; corrected from model atmospheres estimates).
Telluric absorption (yes, there is atmosphere above the Shuttle!).
Flux loss from field astigmatism (extended sources only).
pointing-jitter errors (jitter corrected every 2 secs).

The calibrated data consist of corrections for all these error sources. See the calibration chapter of the HUT data handbook.

8) Did HUT lose sensitivity during its missions?

Yes, the losses were noticeable on an approximately 48 hour timescale, particularly in the far-UV. This is modeled in Figure 5 of Kruk et al. (ApJS, 122, 299, 1999). By the end of the mission the sensitivity of the detector (CsI photocathode) had decreased by 26% at 912 Å and 5% at 1840 Å.

9) What were the differences between HUT1 and HUT2?

The second mission:

lasted longer (16 days compared to 8 days; 205 hours of on-target time vs. 40 hours).
made more observations (385 of 265 targets, compared to 136 of 87 targets).
had greatly improved pointing stability.
had less sensitivity to extreme-UV contamination because of SiC coatings on the optical elements.