About VALD

The Vienna Atomic Line Database (VALD) is a collection of atomic and molecular transition parameters of astronomical interest. VALD offers tools for selecting subsets of lines for typical astrophysical applications: line identification, preparing for spectroscopic observations, chemical composition and radial velocity measurements, model atmosphere calculations etc.

The VALD Electronic Mail Service (VALD-EMS) is the main data transfer protocol for small data sets. For larger data extraction VALD users are advised to use the 'via ftp' option. This web portal is the main user interface to VALD VALD-EMS. It offers full functionality of the extraction tools and flexibility of data access. An alternative user interface and data transfer protocol are offered via the Virtual Atomic and Molecular Data Center (VAMDC). This option allows direct computer access to VALD and many other databases but it lacks some of the functionality that is present in the VALD extraction tools.

Below are the main ideas behind VALD concept that may help you using it in the most efficient way:

• VALD extraction tools are constructed for intelligent selection of data relevant for specific astronomical problem.
• Bulk data transfer via remote access is highly inefficient. For massive extraction (e.g. for computing opacity tables) you should consider hosting a mirror site. Contact the VALD administrator if you are interested.
• VALD is regularly updated with critically evaluated data sets. The VALD project team experts investigate the statistical properties of the data, extensively compare the results obtained with different data sources, and establish the quality rating for each new source which is a basis for data selection. This portal offers you a possibility to create and save an alternative ranking table that would also ensures reproducibility of the extraction.
• VALD data access is free but requires registration. Registration helps us rejecting spam, collecting statistics and informing you about updates. We do not share your registration information with anyone.