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Frequently Asked Questions
(last update: March 29, 2013)
- What is HUT and What Does it Do?
"HUT" stands for the Hopkins Ultraviolet Telescope. It was a 0.9-meter telescope equipped with a far-UV spectrograph that flew on two separate space shuttle missions, along with two other UV telescopes, in 1990 (Astro-1) and 1995 (Astro-2).
It obtained multiple spectra of more than 400 astronomical objects, including solar system objects, cataclysmic variables, supernova remnants, nearby galaxies, and AGN. The first spectral order covers 825 - 1850 Å at a resolution of ~3 Å. Spectra from the second order, which covers 420 - 925 Å, were also obtained for two white dwarfs during the Astro-1 flight.
For more information on the missions, see the About HUT page.
- What is the history behind HUT?
Check out the links at the top of the About HUT page.
- 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.
- What are some major publications using HUT data?
See our page summarizing some of the mission-specific publications.
- How do I retrieve HUT data?
Data retrieval proceeds in much the same way as most other MAST-archived datasets. Go to the HUT Search Help page for instructions and the HUT Search Form for downloading of data. For further information go to the HUT data products page.
- How do I read HUT data?
The FITS files should be readable by any standard FITS I/O library. A summary of some of the most popular ones can be found here. Additionally, you can visit the HUT Extraction Software page, which describes some routines written in C (provided by the HUT team) to extract a calibrated spectrum (cal.fits file) from a photon-list (idf.fits file).
- What are the instrumental error sources in HUT data?
Some sources of systematic errors include:
- 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 spectra have corrections made for all of these error sources. For details, see the paper by Dixon et al. PASP, 2013 that fully describes the data processing.
- 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.
- 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 (275 targets, compared to 90 targets).
- Had greatly improved pointing stability.
- Had less sensitivity to extreme-UV contamination because of SiC coatings on the optical elements.
- Why do some objects have different values in the TARGNAME header keyword?
In general, the TARGNAME header keyword is the name of the object itself. There are a few exceptions to this rule. The most common are situations where the string "_offset" is appended to the name of the object. This usually means the observation corresponds to a measurement of the background. These were obtained by observing more than 6 arcseconds away from the primary target. In this case, the coordinates within the header are of the actual pointing, rather than the primary target.
Some additional exceptions are: - JUPITER - "JUPITER_AURORA" refers to an observation taken near the planet's south polar limb, "JUPITER_EQUATOR" at the planet's equator, "IO_EAST" centered on the leading hemisphere of Io, "IO_WEST" centered on the trailing hemisphere of Io, "IO_TORUS", "IO_TORUS_POS1", "IO_TORUS_POS2", and "IO_TORUS_POS3" all sampling different parts of Io's torus. For full details, see Appendix B in Dixon et al. PASP, 2013.
- NGC1535 - "NGC1535_CSPN" is an observation of the central star within the nebula, while "NGC1535_NEB" is an observation of the nebula itself ~9 arcseconds away from the central star.
- NGC7023 - The star HD 200775 within this nebula was observed by HUT. In addition, a reflection nebula near this star was observed and labeled as "NGC7023 OFFSET".
- RHOOPHAB - This binary system (HD 147933) was to be observed along with the nearby reflection nebula IC 4604. The observations of the binary were never obtained, while the observations of IC 4604 are labeled as "RHOOPHAB OFFSET".
- XI-PER - The star itself was too bright to observe directly, therefore, HUT observed an H2 region 100 arcseconds to the north, and labeled these "XI-PER OFFSET".
- NGC1851 - The TARGNAME value "NGC1851_UV5" refers to a specific, UV-bright star within the globular cluster.
- 47-TUC - The TARGNAME value "47_TUC_BS" refers to a specific, UV-bright star within the globular cluster.
- M13 - The TARGNAME value "M13_BARN_29" refers to a specific, UV-bright star within the globular cluster.
- M3 - The TARGNAME value "M3_VZ1128" refers to a specific, UV-bright star within the globular cluster.
- M67 - The TARGNAME value "M67_F81" refers to a specific blue straggler star in the open cluster.
- SN1987A - The TARGNAME value "SK-69_203" refers to a specific, B-type star near the supernova remnant.
- How do I use the second-order spectra of G191-B2B (HUT109702) and HZ43 (HUT105203)?
No inverse-sensitivity curve is available for the second-order spectra. The extracted spectrum and quick-look plots have units of counts per second. The inveerse-sensitivity curves in the idf.fits files should not be used. For more information, see Section 3.9 and Appendix B in Dixon et al. PASP, 2013.
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