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Knowledgebase : Data Access / Herschel Science Archive > Highly Processed Data Products
To find out about the steps to follow in reducing SPIRE spectroscopy and, in particular, how to carry background subtraction of spectra, there is a Herschel Science Centre short videotutorial that shows you the steps involved and also describes the data products that are available for which experts have carried out background reduction already. You can find the videotutorial here:
https://www.youtube.com/watch?v=O_pqN4VDu9M
This videotutorial describes a useful interactive script for background reduction and shows a practical example of how to carry out background subtraction and the decisions involved in carrying out background subtraction interactively, identifying and eliminating interactively the outliers in background subtraction. It also gives you details of the available expert-reduced background subtracted spectra available as a Highly Processed Data Product.
HIFI spectra can be of two kinds: ON source spectra, in which the keyword "isLine=True) and OFF source, reference position spectra, for which isLine=FALSE. The reference position though may, itself, be contaminated by background emission, compromising the reduced on-source spectrum. The best way to eliminate or, at least, to assess this effect is to examine the OFF source spectra. The Herschel Science Centre has produced a short videotutorial that explains how to examine the OFF spectra. You can find this videotutorial here:
https://www.youtube.com/watch?v=Tpte_3LTL-s
OFF spectra can be different things for different observing modes. The short videotutorial will show you what the OFF spectrum represents for each mode and will take you through a practical example of how to examine and plot the OFF spectrum in the observation context. It will also show you the effects of line contamination in an OFF spectrum when it is used for background subtraction.
If you are an absolutely beginner with Herschel data and want to learn how to do photometry on PACS observations there are two places to start before working with data.
First, you should look at the Quick Start Guide for Photometry (CSG), otherwise known as the PACS Data Reduction Launchpad: Photometry. This will teach you some of the basics of PACS data analysis. It will also guide you towards more detailed documentation that will explore photometry in more depth.
Second, you should consult the Herschel Science Centre short videotutorial on Starting with PACS Photometry. You can find it here:
https://www.youtube.com/watch?v=yLHLA5Jjtiw
The short videotutorial will talk you through the PACS photometry data products that are available in the Herschel Science Archive (HSA) and which products are best for the analysis of what type of object. You will be shown the structure of a PACS photometry observation when downloaded from the HSA and how the filename structure of a product tells you what type of product it is. You will be shown also what Highly Processed Data Products (HPDPs) - also known as "Expert Reduced Data Products" - are available and how they may be used.
There are two excellent starting points for learning how to use PACS spectroscopy data. We recommend strongly that you start by reading the Quick Start Guide to Spectroscopy (also known as the PACS Data Reduction Launchpad: Spectroscopy), which summarises the PACS spectroscopy observing modes, data products, calibration uncertainties and science-readiness of the different PACS spectroscopy products.
There is also a Herschel Science Centre short videotutorial called Starting with PACS Spectroscopy, which will walk you through the basics of PACS Spectroscopy. You can find the short videotutorial here:
https://www.youtube.com/watch?v=rcY487Z9Kyg
This short videotutorial will explain the three basic observing modes for PACS spectroscopy and their uses, how to determine from the Herschel Science Archive (HSA), or from the FITs header in which observing mode an observation was made, detailing the main keywords that users should be familiar with. For each product, you will find out which data products you need and what products are available at different levels for the different observing modes. You will learn what the PACS cubes are and their contents for different modes, PACS data tables and so-called slices for each mode, which are the different presentations of the cubes and tables. You will learn what a PACS spectroscopy observation looks like in the HSA and what post-processing (if any) is required for sources of different sizes. Finally, you will see which Highly Processed Data Products (Expert Reduced Data Products) have been prepared by the experts at the Herschel Science Centre for particularly difficult cases.
Reduction and analysis of SPIRE FTS spectra treats two, generic cases: point sources (sources smaller than 3-4 arcseconds that are effectively a point-source for SPIRE) and extended sources (anything larger than 40 arcseconds). However, there are many sources between these two extremes that can neither be treated as point sources, nor as extended. The immediate consequence for observers is that neither the point source reduction, nor the extended source reduction give a good result: users will see this in the form of a large discontinuity between the two SPIRE spectra ranges.
There is a Herschel Science Centre short videotutorial that shows you how to categorise sources by diameter and how to identify cases in which neither the point source calibration, nor the extended source calibration give a satisfactory result and how to treat these cases. You can find it here:
https://www.youtube.com/watch?v=mxZpHgHVtP4
The short videotutorial will walk you through the basics of SPIRE FTS spectra data reduction, including the need to carry out certain, basic pre-reduction such as to subtract the background first before applying the Semi-Extended Calibration Tool (SECT) to the spectra. It will show you how to set the parameters and, through a practical example, how to make an iterative fit to the effective source diameter. Finally, it will show you the checks that you can carry out to ensure a self-consistent result.
The Herschel Science Archive (HSA) allows multiple categories of searches to be carried out using different criteria. In particular:
- Search by target name.
- Search by coordinates (in a radius around a particular position).
- Search by catalogue (for example, in the Herschel PACS, or Herschel SPIRE Point Source Catalogues, or for data published as a Highly Processed Data Product, or... etc.)
- Search for unpublished observations.
You can find the short videotutorial here:
https://www.youtube.com/watch?v=sHWQqp2zGR4&feature=youtu.be
Highly processed data products are sets of data that have been reduced by experts working for the Herschel Science Centre because they have issues that makes them extremely difficult to reduce optimally by automatic pipeline, or even by a non-expert in interactive mode. The Herschel Science Centre has produced a short videotutorial that gives a guided tour of the different HIFI Highly Processed Data Products (HPDPs) that are available. You can find the short videotutorial here:
https://www.youtube.com/watch?v=AV9HwZYQt_I
The short videotutorial will introduce you to the types of HIFI HPDPs that are available, before showing you the scope and content of each HPDP dataset, with a description and examples of the products that it contains: spectral scans, spectral maps, off spectra (reference position spectra), the HIFI lines catalogue, and flux uncertainty budget tables.
The Herschel Science Archive (HSA) provides a large amount of information in response to a search for observations of a particular target. In particular:
- How many observations there are in the HSA for this target, their status and quality.
- What publications have been produced from each observation.
- What User Provided Data Products are available for each observation.
- What Highly Processed Data Products are available for each observation and how these compare with the standard pipeline products.
- How to filter searches to obtain more, or less information.
You can find the short videotutorial here:
https://www.youtube.com/watch?v=sHWQqp2zGR4&feature=youtu.be
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