Further access options are discussed below
For a list of all services and tables belonging to this service's resource, see Information on resource 'The PPMXL Catalog'
Observers using USNO-B1.0 for the reduction of their CCD frames get positions of their targets which are not on the ICRS. Such positions can neither be used to derive inertial stellar proper motions, nor should they be used for in orbit determinations in the case of solar system bodies. According to 2009DDA....40.1704C, there are millions of minor planet positions based on USNO-B1.0 in recent years.
To aid in reducing these observations to ICRS, we present systematic correction tables from USNO-B1.0 to PPMXL for positions at epoch 2000.0 and for proper motions. The tables give means of the differences in positions and proper motions between PPMXL and USNO-B1.0 in circles of radius sqrt(2)/2 around the centers of 360 by 180 spherical squares covering the sky. The application of these tables is straighforward. Suppose you have an observation (α,δ) based on USNO-B1.0 at epoch T (in years). To locate the corrections in downloaded tables (see below), compute floor(α)+0.5, floor(δ)+0.5 or use the web service.
The conversion to ICRS is given by
In applying these formulae note that they are not rigorous, with the approximations used breaking down close to the poles. Also, be careful when crossing α=0 during the correction.
The full correction table can be downloaded as VOTable or plain text .
Here are maps of the corrections over the entire sky for RA, Declination and the proper motions:
You can access this service using:
This service is published as follows:
local means it is listed on our front page, ivo_managed means it has a record in the VO registry.
Other services provided on the underlying data include:
The following fields are available to provide input to the service (with some renderers, some of these fields may be unavailable):
Name | Table Head | Description | Unit | UCD |
---|---|---|---|---|
DEC | Delta (ICRS) | Declination (ICRS decimal) | deg | pos.eq.dec |
hscs_pos | Position/Name | Coordinates (as h m s, d m s or decimal degrees), or SIMBAD-resolvable object | N/A | N/A |
hscs_sr | Ignored | Ignored | N/A | N/A |
RA | Alpha (ICRS) | Right Ascension (ICRS decimal) | deg | pos.eq.ra |
SR | Search Radius | Search radius | deg | N/A |
The following fields are contained in the output by default. More fields may be available for selection; these would be given below in the VOTable output fields.
Name | Table Head | Description | Unit | UCD |
---|---|---|---|---|
alpha | Center RA | Center for field, RA | deg | pos.eq.ra;meta.main |
d_alpha | PPMXL-USNO, RA | Correction PPMXL-USNO in alpha (Epoch 2000.0) | deg | pos.eq.ra;arith.diff |
d_delta | PPMXL-USNO, Dec | Correction PPMXL-USNO in delta (Epoch 2000.0) | deg | pos.eq.dec;arith.diff |
d_pmalpha | PPMXL-USNO, PM RA | Correction PPMXL-USNO in proper motion alpha*cos(delta) | deg/yr | pos.pm;pos.eq.ra;arith.diff |
d_pmdelta | PPMXL-USNO, PM Dec | Correction PPMXL-USNO in delta | deg/yr | pos.pm;pos.eq.dec;arith.diff |
delta | Center Dec | Center for field, Dec | deg | pos.eq.dec;meta.main |
nob | N | Number of objects the correction is based on | N/A | meta.number |
The following fields are available in VOTable output. The verbosity level is a number intended to represent the relative importance of the field on a scale of 1 to 30. The services take a VERB argument. A field is included in the output if their verbosity level is less or equal VERB*10.
Name | Table Head | Description | Unit | UCD | Verb. Level |
---|---|---|---|---|---|
alpha | Center RA | Center for field, RA | deg | pos.eq.ra;meta.main | 1 |
delta | Center Dec | Center for field, Dec | deg | pos.eq.dec;meta.main | 1 |
d_alpha | PPMXL-USNO, RA | Correction PPMXL-USNO in alpha (Epoch 2000.0) | deg | pos.eq.ra;arith.diff | 1 |
d_delta | PPMXL-USNO, Dec | Correction PPMXL-USNO in delta (Epoch 2000.0) | deg | pos.eq.dec;arith.diff | 1 |
d_pmalpha | PPMXL-USNO, PM RA | Correction PPMXL-USNO in proper motion alpha*cos(delta) | deg/yr | pos.pm;pos.eq.ra;arith.diff | 1 |
d_pmdelta | PPMXL-USNO, PM Dec | Correction PPMXL-USNO in delta | deg/yr | pos.pm;pos.eq.dec;arith.diff | 1 |
nob | N | Number of objects the correction is based on | N/A | meta.number | 18 |
VOResource XML (that's something exclusively for VO nerds)