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Update readme for 1p8 #182

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75 changes: 51 additions & 24 deletions docs/catalog-description.rst
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================================================
THE AXAF Guide and Acquisition Star Catalog V1.7
THE AXAF Guide and Acquisition Star Catalog V1.8
================================================

An all-sky astrometric and photometric catalog
prepared for the operation of Chandra
(formerly AXAF). version 1.7 September 2018
(formerly AXAF). version 1.8 July 2024

Introduction
============
Expand All @@ -13,8 +13,8 @@ The AXAF Guide and Acquisition Star Catalog (AGASC) is presented in
this set of FITS (Flexible Image Transport System) files, and may
be distributed in a variety of formats, including DAT (DDS format)
or CD-ROM (compact disc, read only memory in ISO 9660 format). This
issue, Version 1.7, corresponds to the AGASC as completed
18 September 2018.
issue, Version 1.8, corresponds to the AGASC as completed
11 July 2024.

The primary source of data for the AGASC is the Guide Star Catalog
(GSC) for the Hubble Space Telescope (HST), version 1.1. The release
Expand Down Expand Up @@ -65,6 +65,10 @@ and its error) for red stars by including the i magnitude information
from the AAVSO (American Association of Variable Star Observers)
Photometric All-Sky Survey (APASS) DR9.

Version 1.8 includes improved star positions and proper motions from Gaia
DR3, as well as improved estimated magnitudes derived from Gaia DR3 photometry
and more than 94,000 ACA observed stars.

Organization of the FITS Data Files
===================================

Expand Down Expand Up @@ -118,10 +122,10 @@ numbers XREF_IDx are included from the original x=1-6 catalogs we
have matched.


Summary of the AGASC1.7 Format
Summary of the AGASC1.8 Format
==============================

Each FITS regions table in the AGASC1.7 consists of 3 parts, the
Each FITS regions table in the AGASC1.8 consists of 3 parts, the
primary header, the table header, and the table data. The conventions
for FITS Binary Tables are detailed in Cotton, Tody and Pence (1995,
A&A, 113, 159), or at http://fits.nrao.edu/FITS.html
Expand All @@ -131,7 +135,7 @@ regions tables. That length is 5x2880= 14400bytes. After these 14400
bytes comes star data records.

The data for each star amounts to 122 bytes, in 47 data columns for
AGASC1.7. Default values are -9999 or 0 where no data are available.
AGASC1.8. Default values are -9999 or 0 where no data are available.
Many columns require data; these have no default values. Another
exception is COLOR1, whose default value is 0.7000 for most stars,
or 1.5000 for stars with COLOR1 greater than 1.5000. Details on all
Expand All @@ -151,10 +155,10 @@ for each data item for each star are as follows::
----------------------------------------------------------------
122 bytes per star

Summary of the AGASC Version 1.7 Entries
Summary of the AGASC Version 1.8 Entries
----------------------------------------

Each of the FITS regions files in the AGASC1.7 will contain the
Each of the FITS regions files in the AGASC1.8 will contain the
following fields for each entry::

BYTES NAME - brief description
Expand Down Expand Up @@ -182,6 +186,7 @@ following fields for each entry::
4 - ACT
5 - Tycho-2
6 - GSC-ACT
7 - Gaia DR3

4 EPOCH - float variable identifying the epoch of the ra and dec
measurements. Default value of -9999.0
Expand Down Expand Up @@ -257,6 +262,9 @@ following fields for each entry::
18 0.72 IIIaJ + GG385
21 0.00 PPM V mag
22 1.00 PPM B mag
23 Gaia DR3 G mag
24 Gaia DR3 Rp mag
25 Gaia DR3 Bp mag

1 MAG_CATID - unsigned integer identifying the source of the
mag, mag_err, and mag_band. Codes are as follows:
Expand All @@ -268,13 +276,15 @@ following fields for each entry::
4 - ACT
5 - Tycho-2
6 - GSC-ACT
7 - Gaia DR3
100 - Chandra ACA estimated magnitude (only via agasc package query)

4 COLOR1 - float variable expressing the cataloged or estimated B-V color,
used for mag_aca, in mag. If no colors are available, the default
value is 0.7000. If Tycho-2 data show colors redder than
(B-V)=1.5, then the default value is 1.5000. True cataloged
color values are stored in COLOR2.
value is 0.7000. If the color is derived from Tycho-2 (C1_CATID=5) and
that color is redder than (B-V)=1.5 then COLOR1 is set to 1.5000. This
is the case for about 21,000 stars in AGASC 1.8. True cataloged color
values are stored in COLOR2.

2 COL0R1_ERR - short integer expressing the error in color1 in units of
0.01 mag. Default value of -9999.
Expand All @@ -287,7 +297,7 @@ following fields for each entry::
For Tycho catalogs, this is the Tycho BT-VT color.
Default value of -9999.0

2 COLOR2_ERR - short integer expressing the error in color2, iun
2 COLOR2_ERR - short integer expressing the error in color2, in
units of 0.01mag. Default value of -9999.

1 C2_CATID - unsigned integer identifying the source of color2 and
Expand Down Expand Up @@ -355,9 +365,8 @@ following fields for each entry::
brightest star within 321" of this star, and this star, in units
of 0.01 mags. Default value of -9999.

4 XREF_ID1 - long integer which is the star number in the
AGASC Version 1.0 (= GSC1.1). This is not a unique identifier.
Default value of -9999.
4 XREF_ID1 - long integer with the highest significant 32 bits of the Gaia DR3 ID.
Default value of -1.

4 XREF_ID2 - long integer which maps the entry to that in the PPM.
Default value of -9999.
Expand All @@ -368,16 +377,18 @@ following fields for each entry::
4 XREF_ID4 - long integer which maps the entry to that in the Tycho Output
Catalog (TYC3). Default value of -9999.

4 XREF_ID5 - long integer which maps the entry to that in a future
catalog. Default value of -9999.
4 XREF_ID5 - long integer with the lowest significant 32 bits of the Gaia DR3 ID.
Default value of -9999.

2 RSV4 - short integer reserved for future use. Default value of -9999.
2 RSV4 - short integer which is the star number in the
AGASC Version 1.0 (= GSC1.1). This is not a unique identifier.
Default value of -9999.

2 RSV5 - short integer reserved for future use. Default value of -9999.

2 RSV6 - short integer reserved for future use. Default value of -9999.

History of the AGASC Version 1.7
History of the AGASC Version 1.8
================================

The primary objective of the Chandra Aspect Camera Assembly (ACA) is to
Expand Down Expand Up @@ -759,19 +770,35 @@ information, V - i aka COLOR3 (APASS) in AGASC 1.7. COLOR2 (Tycho)
combined with COLOR3 (APASS) resulted in improved calibration of the
red spoiler stars.

Gaia DR3
--------

The Gaia DR3 catalog is the third data release from the European Space Agency's (ESA) Gaia mission.
The Gaia mission is designed to measure the positions, distances, and proper motions of stars with
unprecedented accuracy. We cross-matched the AGASC catalog with the Gaia DR3 catalog, and calibrated
the ACA magnitude estimates of more than 94,000 observed stars with the corresponding Gaia
magnitudes.

More details concerning Gaia can be found in the following resources:


1. Gaia Data Release 3, A. Avllenari et al. 2024, A&A, 674, A1
https://doi.org/10.1051/0004-6361/202243940
2. https://www.cosmos.esa.int/web/gaia-users/archive/gdr3-documentation
3. https://gea.esac.esa.int/archive/


Acknowledgements
================

The AXAF Guide and Acquisition Star Catalog version 1.7 was prepared
from AGASC1.6 and AAVSO (American Association of Variable Star Observers)
Photometric All-Sky Survey (APASS) DR9, primarily by Malgosia Sobolewska,
The AXAF Guide and Acquisition Star Catalog version 1.8 was prepared
from AGASC1.7 and Gaia DR3, primarily by Javier G Gonzalez,
Tom Aldcroft, and Jean Connelly. Thanks to the entire Star Selection and
Aspect Working Group for its input in the development and testing of this
catalog. The Chandra X-ray Center is supported through NASA Contract
NAS8-39073. Information about Chandra and the Chandra X-ray Observatory
Center may be found on the WWW at http://chandra.harvard.edu/
Detailed information about the catalog and its construction can be
obtained from the Chandra aspect web page at
https://cxc.harvard.edu/mta/ASPECT/agasc1p7 or by emailing:
https://cxc.harvard.edu/mta/ASPECT/agasc1p8 or by emailing:
aspect_help@cfa.harvard.edu
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