Herschel Data Search Documentation

The Herschel Space Telescope

The Herschel Space Telescope is the fourth Cornerstone mission in the European Space Agency's Horizon 2000 program. Ten countries, including the United States, participated in its design and implementation. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. The telescope was launched on 14 May 2009 and remained operational until 29 April 2013. It performed photometry and spectroscopy in the 55 - 671 µm range, bridging the gap between earlier infrared space missions and ground-based facilities.

Herschel was designed to observe the 'cool universe'. One of its major objectives was to discover how the first galaxies formed and how they evolved to give rise to present day galaxies like our own. Additional targets for Herschel included clouds of gas and dust where new stars are being born, disks out of which planets may form and cometary atmospheres packed with complex organic molecules.

For more information about the mission, please see the webpages from the NASA Herschel Science Center

The Herschel Instruments

Herschel had three main scientific instruments on-board: the Photodetector Array Camera and Spectrometer (PACS), the Spectral and Photometric Imaging Receiver (SPIRE), and the Heterodyne Instrument for the Far Infrared (HIFI).

Photodetector Array Camera & Spectrometer

The Photodetector Array Camera & Spectrometer (PACS) provided Herschel with capabilities for spectroscopy and imaging/photometry in the 55-210 microns range. The PACS instrument comprised two sub-instruments offering two basic and mutually exclusive modes in the wavelength band 55-210 microns:

• Imaging dual-band photometry (60-85 microns or 85-130 microns and 130-210 microns) over a field of view of 1.75 x 3.5 arcmin, with full sampling of the telescope point spread function (diffraction/wavefront error limited).
• Integral-field spectroscopy between 55 and 210 microns with a resolution of ~75-300 km/s and instantaneous coverage of ~1500 km/s, over a field of view of 47 x 47 arcsec.

Three different Astronomical Observing Templates (AOTs) were defined and implemented to perform astronomical observations with PACS: one generic for photometry/mapping and two for the spectrometer:

• Photometry: In this AOT the PACS photometer observed in the blue channel, either in the 60-85, or in the 85-130 micron band, depending on the requested filter combination, while in the red channel the 130-210 micron band was observed simultaneously. Observing modes offered a choice of mapping modes, combined with specific background subtraction techniques.
• Line(s) spectroscopy: In this AOT the PACS spectrometer observed individual spectral lines. Depending on the requested grating order, the short-wavelength array observed in the 51-73 micron, or 70-105 micron band, while the long wavelength red array observed in the 103-220 micron band. The observer could select both chopping/nodding and unchopped grating scans, in combination with pointed or mapping observing modes.
• Range(s) spectroscopy: In this AOT the observer could specify freely the wavelength range to be explored, or could choose the Spectral Energy Distribution (SED) mode offering a predefined range that will cover the entire bandwidth of the selected orders.

The plural in line(s) and range(s) indicates that several lines or wavelength ranges could be observed within the scope of one AOT.

Spectral and Photometric Imaging Receiverr

The Spectral and Photometric Imaging Receiver (SPIRE) performed photometry and spectroscopy observations from ~60 to ~672 microns. SPIRE contains a three-band imaging photometer and an imaging Fourier-Transform Spectrometer (FTS), both of which used bolometer arrays operating at 0.3 K and are coupled to the telescope by hexagonally close-packed conical feedhorns. Three bolometer arrays were used for broad-band photometry (Resolving power ~3) in spectral bands centered on approximately 250, 350 and 500 microns. The same 4 x 8 arcmin field of view was observed simultaneously in these three bands through the use of two fixed dichroic beam-splitters. Signal modulation could be provided either by SPIRE's two-axis Beam Steering Mirror (BSM) or by scanning the telescope across the sky. An internal thermal source was available to provide a repeatable calibration signal for the detectors (and could also be seen by the FTS detectors).

There were two AOTs available for SPIRE: one for doing photometry with the Photometer and one for using the Spectrometer to do imaging spectroscopy at high, medium or low spectral resolution.

The SPIRE photometer AOT could be used with three different observing modes:

• Point Source Photometry: This mode was for photometric observations of isolated point sources. It used chopping, jiggling and nodding, observing the source at all times.
• Small Map Photometry: This was for sources or areas smaller than 4 x 4 arcmin. The guaranteed observed area was a 4 arcmin diameter circle. Chopping and nodding were used.
• Large area or extended source mapping: This mode was for mapping sources larger than a 4 arcmin diameter circle, or to cover large areas of sky. The map was made by scanning the telescope.

The SPIRE Spectrometer AOT was used to make spectroscopic observations with the SPIRE Fourier Transform Spectrometer. The spectrometer could be used to take spectra with different spectral resolutions. These spectra could be measured in a single pointing (using pixels within the field of view of the instrument) or in larger maps which were made by moving the telescope in a raster. For either of these, it was possible to choose sparse, intermediate, or full Nyquist spatial sampling.

In Parallel Mode, PACS and SPIRE operated in photometry mode simultaneously, carrying out large-area mapping observations. PACS took data in its red band (130-210 microns) and in one of the blue bands (60-85 microns or 85-130 microns) while SPIRE observed in its three photometric bands (250, 350 and 500 microns). The SPIRE PACS Parallel Mode has its own AOT and the two instruments were operated in a way that the spacecraft infrastructure was optimally used.

The Parallel Mode AOT was offered with only one observing mode. Scanning was the most compatible operating mode of PACS and SPIRE. Scan maps were the default for PACS to map large areas of the sky, for galactic as well as extragalactic surveys. SPIRE always operated in scan mode for large mapping observations.

Heterodyne Instrument for the Far Infrared

HIFI is the Heterodyne Instrument for the Far Infrared. It was designed to provide spectroscopy at high to very high resolution over a frequency range of approximately 480-1250 and 1410-1910 GHz (625-240 and 213-157 microns). This frequency range is covered by 7 "mixer" bands, with dual horizontal and vertical polarizations, which could be used one pair at a time.

There were four spectrometers on board HIFI, two Wide-Band Acousto-Optical Spectrometers (WBS) and two High Resolution Autocorrelation Spectrometers (HRS). One of each spectrometer type was available for each polarization. They could be used either individually or in parallel. The Wide-Band Spectrometers covered the full intermediate frequency bandwidth of 2.4 GHz in the highest frequency bands (bands 6 and 7) and 4 GHz in all other bands. The High Resolution Spectrometers had variable resolution with subbands sampling up to half the 4GHz intermediate frequency range. Subbands had the flexibility of being placed anywhere within the 4 GHz range.

For HIFI, three AOTs were available:

• Single Point: Used to observe science targets at one position on the sky.
• Mapping: Used to cover extended regions.
• Spectral Scanning: To survey a single position on the sky over a continuous range of frequencies selected within the same Local Oscillator band by the user.

The Herschel Science Archive (HSA)

The HSA contains over 60 000 individual observations taken during the operational phase of the Herschel Space Telescope. The Observatory performed the observations in the context of the Key, AO-1, AO-2, Must-do, and filler programs. A list of publications cross-correlated with observation ID is available.

Data are downloaded as tar-balled directories, containing XML, txt, and FITS files. Information about the format of the data download is available from the Product Definitions Document. In particular, the format the instrument datasets is described in the relevant sections (for PACS, SPIRE, and HIFI) of that document.

The archive contains raw and reduced data, and with this interface the user can download all the data associated with a given observation ID. To download only certain parts of the data please see the HSA interface at the HSC.

All observations are made public 6 months after they are performed. From this interface, the user can only download public data.

The columns in the results table have the following meaning: