NExScI PTI Archive Description

This archive contains data from the visibility amplitude mode of the Palomar Testbed Interferometer. The archive was originally built as a technology testbed for the Keck Interferometer, but has been used for scientific observations since 1997. PTI is currently operated by the NExScI on behalf of the PTI collaboration.

Download PTI data here .

In order to create a database useful to the entire astronomical community, a set of minimum criteria were established for inclusion in the database. Data which did not meet these criteria are still preserved at NExScI, but are not available in the on-line database. This page describes the modifications made to the original PTI data files before inclusion in the database. The intrinsic measurements (visibility amplitude, photon flux) have NOT been altered.

Archive Contents

The archive currently contains data from 1753 sources over 1577 nights. Data from all nights are available to the public. The PTI sensitivity limits are roughly V<11 and K<6 with approxiamate declination limits of -10 to 60 degrees. Science targets observed with PTI cover a number of galactic astrophysical topics, including (but not limited to) binary orbits, radii of main sequence, giant and supergiant stars, and circumstellar material around evolved and young stars.

Year Number of observing nights

Data Proprietary Period

PTI is no longer an active interferometer, and the proprietary period for all data has ended.

Data Validation

The science data were evaluated against the following limits. Data with values outside these bounds are not included in the archive.

  • Photon counts (fringe, foreground, background): 0 to 1e8 DN
  • Visibility (V2): 0 to 5
  • Ratio correction: 1 to 10
  • Wavelength: 1.0 to 3.0 microns
  • Fractional time: 0 to 1.0 (Fraction of time the fringe tracker was locked during the requested integration time of 120 seconds)

Source Names

Constraints in the real time observing software at PTI limit source names in observing files to start with a limited set of three letter acronyms (e.g. HDC, HBC, MWC). This requirement led to the use of many source names not recognized by the SIMBAD database. To increase the usefulness of the database, ALL source names have been converted to SIMBAD-compliant designations, except that internal spaces have been eliminated (i.e. HBC 123 is HBC123 in the PTI database). In particular, this means that all HDC sources (the PTI real time system designation for the HD catalog) are now called HD. However, you can search the database using HDC names. The original source names are available by downloading the original files (see below).

Source Designations and Catalog Files

Observation sequences at PTI generally consist of interleaved observations of target and calibrator sources. Calibrators are generally chosen to be unresolved or of a known angular diameter. All sources in the archive are categorized as either target (TRG), calibrator (CAL) or engineering (not available to the public). Whenever possible, these designations were taken from the original file. However, on many nights, particularly in the early years of PTI operations, the source designations were not saved, and a best effort has been made to properly designate sources as targets or calibrators.

The TRG/CAL designation does not affect the measurement data, only how the archive retrieves data as it is possible to request automatic retrieval of all the calibration data for a science target. Users of archive data should examine sources listed as calibrators as part of the data calibration process. In particular, it should be noted that individual stellar sources have been used as a target on some nights, but as a calibrator on others. It has also occured that calibrators are later discovered to be bad (e.g. binary). See the bad calibrator list for bad calibrators contributed by PIs.

File names

The Level 1 file names have been converted to a format of yyyyddd where yyyy is the year and ddd is the day of the year in UT time.

Original files

The original files as produced by the PTI pipeline are available online in a gzipped tar file. Data can be download for the entire archive, by year, or by individual observation date starting from this web page.

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