The Portal enables searches of a few special collections, most of which can be selected from the collection menu.

Search Virtual Observatory Collections

The Virtual Observatory (VO) is composed of electronic archives from many astronomical centers around the world. These archives contain a wide variety of data and other resources, including catalogs, images, and spectra. The results of a VO search will look similar to that shown in the figure below.

Searching the VO with the Portal differs from a basic search in a few important respects:

1. Searches are only by target name or sky coordinates; there is no "advanced search" option.
2. The resuts of a VO search are not observations of a target. Rather, the table rows contain metadata about each VO resource, including the type of data objects (images, spectra, catalog).
3. To access science data, click the Data Load button, which in effect initiates a search of that resource to return the associated science data. This action is referred to as a drill-down, and is a key component of using the Portal to explore multi-tiered data hierarchies, such as those in the VO.
4. Click the file iconin a given row to retrieve the science metadata (in XML format) associated with that resource.
5. Optionally download the metadata in the results table to a file on your local system by clicking the export button . Select your desired output format in the Export dialog.

Search the Hubble Source Catalog

The Hubble Source Catalog (HSC) consists of photometry of sources that have been imaged with one or more instruments on HST. MAST supports multiple ways to search the HSC; the Portal allows searches in a circular region around a user-specified position on the sky (a cone search). Searching the HSC is a form of catalog search, and the chapter on Demos and Tutorials shows several science-motivated example searches.

As with VO searches, an HSC search returns results that differ from a basic search in a few important respects:

1. Searches are only by target name or sky coordinates; there is no "advanced search" option.
2. It is possible to retrieve brightness measurements that were made using a finite aperture (MagAper2), or an approximate total brightness (MagAuto). See Whitmore, et al. 2016 for details.
3. The results of an HSC search are not exposures of a target. Rather, the table rows contain photometric measurements and other metadata about each source.
4. It is possible to access the images that contributed to each photometric measurement by clicking the Data Load icon. These images can be overlayed in the AstroView tool by clicking the Overlay icon.
   
   1. To retrieve one or more of the contributing images, click the Download Basket icon; or click the File icon to instantly download a single image.
5. Optionally download the photometric results table (or selected rows within the table) to a file on your local system by clicking the Export button . Select your desired output format in the Export Dialog.

Create a DOI

A Digital Object Identifier (DOI) is a persistent link to a resource on the internet, and is often used in astronomy to provide access to specific data collections. Investigators can use a special instance of the Portal to generate a DOI for one or more datasets hosted by MAST. This will generate a permanent link that may be included in a research paper to refer to the data that were analyzed.

DOIs for many collections, including High-Level Science Products, certain catalogs, and Kepler/K2 campaigns have already been created. To use them in your work, see the detailed DOI documentation. To create a new custom DOI for data you wish to publish, see the following how-to video, or follow the written instructions below.

Create-a-DOI walkthrough video.

	Instruction	Notes
1	Navigate to the DOI Portal at: https://mast.stsci.edu/portal/Mashup/Clients/DOI/DOIPortal.html. You must login to the Portal to create a DOI.
2	Execute a Portal search for observations that include the data to be published.
3	Select rows in the results table that correspond to the specific observations to which the DOI should refer, and place them in the download basket. If necessary, make multiple searches and place relevant observations from each in the download basket.
4	Click the My DOI Basket button to bring up Download Manager, which will look something like the picture below.
5	Select the rows corresponding to the desired observation IDs and filters, then click the button to create a DOI. If you need to update an existing DOI you created, contact MAST.
6	Fill in the DOI requested metadata in the dialog box, then click the Create DOI button.

Load a DOI

There are three ways to access the data that a MAST DOI points to:

1. Resolve the DOI in your browser. For example, for the TESS Input Catalog (doi:10.17909/fwdt-2x66, from the list of pre-made MAST DOIs), the following URLs will both work:
          https://dx.doi.org/10.17909/fwdt-2x66
          https://archive.stsci.edu/doi/resolve/resolve.html?doi=10.17909/fwdt-2x66
   These will lead you to a landing page, where you can follow a link to "display data":

   Depending on the nature of the data cited by the DOI, the "display data" link will either load a set of observations in the Portal, or lead to another webpage with information about retrieving the data.
   
   

2. You can search for a MAST DOI's observations using the general-purpose MAST Portal as follows. This will only work if the DOI you wish to access points directly to observations in the MAST Portal. (So it won't work for the TESS Input Catalog pre-made DOI we used above. We'll instead use 10.17909/t9-z1c2-ye93, a DOI created using the MAST DOI Portal by the authors of a paper who wanted a permanent reference to the data that they employed. You would typically find a DOI like this one by encountering it in a paper.) 

   	Instruction	Notes
   1	Navigate to the Portal at: https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html
   2	Under the Select a collection... dropdown menu, choose Observations in a DOI.
   3	Enter the DOI string (e.g., 10.17909/t9-z1c2-ye93) into the search field, and click Search.

   This method will not work for certain pre-made MAST DOIs for catalogs, HLSP webpages, or bulk mission data, which point to informational webpages or custom download scripts even when the data actually are available in the Portal.

3. You can use the MAST DOI Portal view any DOIs that you have created using your account. You will not be able to download data using this method; see above for data retrieval options.

   	Instruction	Notes
   1	Navigate to the DOI Portal at: https://mast.stsci.edu/portal/Mashup/Clients/DOI/DOIPortal.html. You must login to the Portal to see the list of DOIs that you have created.
   2	Select Show my DOIs in the Search by... dropdown menu, and click the Load All button.
   3	Select the Show DOI Data entry in the Actions column.

Other Searches

A few special searches enable access to lesser-used or mission-specific collections, which are listed in the table below.

For Further Reading...

• DOI documentation