Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Hipparcos catalogue question

  1. Oct 15, 2006 #1

    I have questions related to the hipparcos catalogue. I like to know what kind of star-properties it is possible to extract from this catalogue.

    I was already at the hipparcos-website to try to figure it out myself, but as I am anything else than an expert on the matter, I got very confused about all the attributes in the catalogue. I hope someone here can help me out a little...

    As far as I know, I can get the star's distance and its luminosity and of course position from the catalogue. What I like to know is, can I get the following properties also?

    -Star type (white dwarf, neutron star, red giant, multiple star system, ...)
    -velocity(transverse / radial)

    I know this is somewhat of a general question, but Im really out in the wind here, trying to get a basic Idea of the whole thing, on whats possible and whatnot. Also can I get everything I get out of the hipparcos catalogue out of the Tycho catalogue, only less accurate?

    Any help would be great, and really appreciated!
  2. jcsd
  3. Oct 15, 2006 #2


    User Avatar
    Science Advisor

    I am not an expert, but I have already used this hipparcos query form. It contains the measured data by hipparchos and thus you can find there photometric and astrometric information, but not any (post-processed) information that infers about properties of the stars from the measured data. So, additionally to the magnitude and position, you can find there the parallax and the proper speed. The other information you ask for is not available there.
    Last edited: Oct 15, 2006
  4. Oct 15, 2006 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As hellfire said, HIPPARCOS only reports on the parameters it directly observed, and some that are directly derivable. That's the nature of surveys - they aim to report only on what they directly observe.

    Some of the other parameters you are interested in are available in other catalogues (radial velocities and some kind of effective temperature can be determined directly from spectra, for example), but others are model dependent, and will come with a wide range of uncertainties (e.g. masses and diameters are much more accurately estimated for (certain kinds of) binaries than for single stars).
  5. Oct 15, 2006 #4
    Thanks for your help.

    So if I have understood it correctly, temperature and radial velocity is derivable from the data within the hipparcos catalogue?
  6. Oct 15, 2006 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member


    They are derivable from the spectra of stars; HIPPARCOS did not observe spectra.

    An estimate of the radial velocity comes from the shift of the lines in the spectra - towards the blue or red - corrected for the motion of the observatory, at the time of the observation, with respect to the solar system barycentre. In the case of binaries, a correction for the motion around the common centre of gravity may also be applied (assuming it can be determined).

    An estimate of some kind of temperature comes from either an analysis of the strengths of lines, in relevant series, or a general fit of the continuum. These may give different estimates (the lines and continuum may come from different regions of the star), and in any case are only valid in a somewhat narrow sense (think of it like this - what is 'the temperature of the Earth'? There is no one single answer that has general meaning).
  7. Oct 15, 2006 #6
    ok, thanks for the explanation. As I read in the documentation of the Hipparcos data, it has astromertic and photomertic data in the catalogue. Do you happen to know what the photometric data is good for then? I know there's a spectral type included in the data also (star class...), is this based on photometric data?
  8. Oct 17, 2006 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The photometric data (IIRC, there are two sets) simply gives a consistent (?), well-defined value for the apparent magnitude of the star, at a particular epoch (or epochs, if observed more than once, as most of the stars were).

    That it is a consistent dataset is very valuable; it provides (potentially) a means of calibrating the ground-based photometric data, which suffers from a wide range of (mostly very well-known) systematic and random errors.

    The spectral class data comes from other sources (IIRC, the catalogue lists them).
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?