Archive Catalogues

Introduction

The ASA and Archive will support the concept of catalogues of information. Applications of these would include the calibrator database, spectral line catalogue and source catalogue. Here we are starting to develop the requiremens for these catalogues.

Spectral Line Catalogue Discussion

The Calibrator Catalogue

Requirements

1. There will be a catalogue which contains details of sources for use as calibrators of instrumental phase, amplitude, flux, pointing, delays, astronomical holography and bandpass for ALMA.

2. These calibrators may include both distant objects, relatively stationary, objects (stars, galaxies, etc) and solar system, moving, objects, including planets, satellites of planets, KBOs and asteroids.

3. For each source the catalogue will contain:
   1. sufficient information to determine the position of the object and its uncertainty. This may include the results of measurements of the position and proper motion or a way of retrieving the object's position using an appropriate ephemeris,
   2. sufficient reference information to be able to determine the origin of this positional information,
4. It can be indicated in the catalogue that sources are continuum, polarisation, absolution flux or spectral line calibrators, or any combinations of these.

5. For continuum calibrators, the catalogue will contain:
   1. the flux of the object (and its uncertainty) and the frequency at which this flux has been measured and the bandwidth and correlator setup used for the measurement,
   2. sufficient spectral information (and temporal information if the source varies periodically) about the source to predict its flux at another frequency at some current or future time,
   3. information on the source size and structure including usable baseline range at different frequencies (with an option for graphical representation of this information as an image or plot of amplitude vs. uv distance) ,
   4. details of the polarisation of the source and the frequency at which this information is valid and its structure and time history,
   5. source velocity
6. For spectral line calibrators, the catalogue will contain:
   1. the name of the spectral line/lines for which the source is a calibrator and its frequency,
   2. a spectrum showing the spectral line,
   3. the line velocity, integrated intensity and width, (and their uncertainties),
   4. information of line free velocity ranges which can be used for baseline subtraction or generating a continuum measurement,
   5. information on the source size and structure,
   6. details of the time history of these parameters

7. For polarization calibrators, the catalogue will contain:
   1. a description of source polarization.
   2. the frequency at which this information is valid
   3. details of the time history of these parameters

   Note

   for the three items above there can be multiple entries (corresponding to different frequencies/lines) for any given source.

8. All entries in the catalogue which relate to observed quantities will include the date and time of the observation.

9. For all entries in the catalogue, the catalogue will contain sufficient reference information to be able to trace the history of the information in the catalogue.

10. The catalogue will contain a time history of past flux and position measurements for each source.

11. The catalogue will be searchable by combinations of constraints on
    1. source position,
    2. flux,
    3. spectral line,
    4. angular distance from a given position on the sky,
    5. elevation at a specified date/time (IAT or LST)
    6. calibrator type (i.e. spectral line, continuum, polarisation, absolute flux etc)
    7. usable uv range (or usability for a particular antenna configuration)

12. The catalogue will contain flags and descriptions describing the quality of each object as a calibrator of a particular type. For example this information might include an indication that a new source or a source from a survey at a different wavelength has potential as an ALMA calibrator (but has yet to be observed) or that this particular source has the most constant (or predictable) submm flux of any source in the sky, or that this source is useful for cross frequency band calibration, etc.

13. Any entries in the catalogue (positions, images, spectra or other information) will contain sufficient information to allow the user to retrieve the ALMA data from which the information was derived. This will be important to allow, for example, a user to investigate the strength of a spectral line as a function of uv distance.

    Other Points still be addressed:

    i) Planning parallactic angle coverage for polarization work - function of HA and Dec rather than instantaneous elevation

    ii) Need to consider single-dish calibrators too

    iii) Need to think about ACA requirements

    There may well also be a need for a catalogue of potential calibrators too. Although this may be handled using the quality information in the calibrator catalogue.

    The Source Catalogue

    Requirements

    1. There will be a catalogue which contains details of sources observed, or to be observed, with ALMA.
    2. For each source the catalogue will contain:
       1. sufficient information to determine the position of the object and its uncertainty. This may include the results of measurements of the position and proper motion, user entered values or a way of retrieving the object's position using an appropriate ephemeris.
       2. sufficient reference information to be able to determine the origin of this positional information

    3. The source positional information must include details of the reference frame in which the position is defined.
    4. For each source the catalogue will contain the source velocity (and how this velocity is defined).

    5. There will be details of the velocity range of line emission towards the source (i.e. a measurement/estimate of the source maximum line width).
    6. The catalogue will be searchable by
       1. position
       2. source name
       3. angular distance of source from a give position on the sky

    -- GaryFuller - 10 May 2005 (including some comments from RobertLaing)

    Summary of comments from SSR

    Calibrators:

    a) Add time/date of observations of calibrators - Done

    b) Is one spectrum of any molecular line sufficient as sources are likely to be resolved

    It was suggested that the catalogue include multiple spectra or the spectrum as a function of uv distance.

    One point to realise is that for many sources in the catalogue there will be spectra of multiple lines (a good spectral line calibrator is likely to be good for a range of lines) and potentially including spectra vs uv distance for many lines may add a lot of volume to the catalogue. I would prefer a single spectrum with the source size information. This will of course include a link to the original data so that a user can always go back to produce a spectrum at the resolution of interest.

    Spectral line:

    a) Add some information about line strengths

    Several options were suggested, but it would appear that the most useful would be to look at existing surveys. However i would argue that the spectral line catalogue is not the place to store the results of existing surveys. This is something that ObsPrep should provide, not the archive. ObsPrep could of course choose to store the results of any existing spectral surveys in the archive in some format, possibly a catalogue of its own.

    Source:

    a) Not only sources to be observed but also actually observed.- Changed.

    Mark comments below about the automatic querying of the catalogue by the dynamic scheduler. This raises the question of whether there is any particular information needed by the scheduler which is so far missing from the requirements.

    -- GaryFuller - 1 June 2005 Summary of comments from SSR plus minor changes to reflect these

    comments on the calibrator catalogue specifications

    a) point source and flux variability

    I think a parameter rating how 'point source' a calibrator is should be included (e.g., qualityPtSource : measuring the flux percentage contained in extended structures). Similarly, a parameter rating how variable the calibrator is (e.g., variabilityScale : giving an idea on the how fast the flux change) should be included.

    b) linear polarization

    May be a direct measure of the percentage of linear polarization (on top of the measurement of Stokes Q and U) should be given too (e.g., linPol) in order to evaluate more easily 'good' polarization calibrators ?

    -- SandraEtoka - 10 Aug 2005

    Some Notes on the Calibrator Database from Mark Holdaway:

    On Single Dish Calibrators:

    The 3-5% flux scale accuracy will be bad for making high fidelity mosaic images. While we might not be able to overcome the uncertainty in the flux scale, we should be able to make the total power and interferometer flux scales consistent, either by some sort of cross-self-calibration algorithm than matches up the flux of the target source in the overlapping regions of the fourier plane for the single dish and interferometers, or by explicit calibration.

    If we use explicit calibration (which i think we have to count on), we need to observe an object which is bright at the observing frequency, and compact enough to be unresolved for both the single dish and several of the shortest interferometer baselines. At low frequencies, the quasars are a good candidate. At the highest frequencies, where ALMA noise is increasing and the quasar flux is falling, a some sort of compact thermal object may be better.

    The same cross-calibration requirements will apply to the ACA. We basically have three separate instruments (ACA interferometer, ACA total power, ALMA interferometer) that will all need to be calibrated, sometimes to better than 1% w.r.t. each other.

    Fast Switching Cross-Band Calibrators

    Above 300 GHz, phase calibrators will likely be observed at 90 GHz, with the phase solutions scaled up to the target frequency. However, there will be differential instrumental phase drifts between 90 GHz and the target frequency, so every 5-10 minutes we will need to calibrate out that cross-band instrumental drift. As this is an instrumental cal, we don't need to be close to the target source on the sky -- ie, we can go 20 degrees over to get a source which is really bright at both the target frequency and 90 GHz.

    While the proposed calibrator information is sufficient to deal with this, it may be useful to add an additional tag, like "suitable for cross-band calibration up to SOME_FREQ".

    Proto-Database? Self-updating Database?

    While the flux calibrators and other calibrators will be known about in detail long before YOUR OBSERVATIONS, the nature of the phase calibrators may not be known in advance. The phase calibrators need to be much closer to the target source, and will be much fainter, so there will be lots of them.

    One possibility is that there will be a list of previously known objects which haven't been evaluated as to their usefulness as calibrators (ie, a proto-calibrator database) -- if there are no good phase calibrators close enough to the target source, these could be observed in advance of the target observations (this had been in the plan at some point, I don't know if it still is). When observed, these sources would migrate into the calibrator database.

    Another way to do things would be to have all of these objects in the calibrator database and to keep tabs on them (the Quasars will be quite variable). So, every time a calibrator is observed at a given frequency as part of an observing project or for evaluation for its suitability for a project, the flux and resolution information will be automatically updated in the calibrator database.

    Again, this basically fits into the framework of what has been written.

    Dynamic Scheduling Interaction with Calibrator Database

    In addition to human browsing capability of the database, the database needs to be easily accessed by computer programs, such as the program which is driving dynamic scheduling, which might querrie the database to determine the optimal calibrator for observing some source at a specific time and atmospheric conditions.

    -- MarkHoldaway - 20 Apr 2005

    -- GaryFuller - 21 Nov 2005 - Started separation in to separate pages for each type of catalogue