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 HSOY Catalog'
The HSOY catalog is a common reduction of PPMXL and Gaia DR1. It essentially applies the technique discussed in 2010AJ....139.2440R, with PPMXL filling the role of USNO-B and Gaia DR1 filling the role of 2MASS. The concrete implementation is fairly different, though. Interested users are referred to the HSOY resource descriptor (this is a DaCHS file, but actual processing is written in SQL), in particular the add_gaia element.
Like Gaia DR1, HSOY is primarily published through a TAP service; the primary site is ivo://org.gavo.dc/tap with the access URL http://dc.g-vo.org/tap.
For simple tasks, there is an IVOA cone search service at http://dc.g-vo.org/hsoy/q/q/scs.xml (browser interface at http://dc.g-vo.org/hsoy/q/q/form).
If you insist, the catalog content can also be downloaded in the form of an xz-compressed Postgres ASCII dump. This is a 40 GB download, and you'll probably spend more time making this useful for you than you'd spend learning ADQL and just using TAP. If you do pull the dump, do, you will find the the metadata (including the column sequence) at http://dc.g-vo.org/tableinfo/hsoy.main. To get this a bit more machine-readably, run SELECT TOP 1 * FROM hsoy.main on our TAP service.
The HSOY catalog contains 583'001'683 objects; this is significantly less than both the roughly 9e8 of PPMXL and the roughly 1.2e9 of Gaia DR1. The bulk of the objects missing in HSOY versus PPMXL should be non-stellar detections and failed matches PPMXL inherited from USNO-B1, but of course the inhomogeneous coverage of Gaia DR1 can be expected to play a role, too.
Positions are given for epoch J2000.0 in ICRS (as defined by Hipparcos via PPMX). Since Gaia astrometry is so precise, the mean epochs are fairly close to J2015 for almost all stars (mean: around 2014.8), even though many stars have observations going back to the 1950s (and older, for PPMXL's bright end is PPMX, which contains even older observations). This means that the positional errors given do not apply at J2000; formal errors in RA and Dec are of the order of 0.1 arcsec for most objects (tighter estimates can be derived fromt the errors in proper motion).
Since the Gaia position is so dominant, the mean error in position at mean epoch is of the order of the DR1 positional errors (about 3 mas averaged over the magnitude bins, much better at the bright end, much worse at the faint end).
Mean formal errors in proper motion at mean epoch range between better than 1 mas/yr for bright stars to about 5 mas/yr near the faint end. Note that these are really formal results of a simple least-squares reduction. They cannot be considered as absolute accuracies as PPMXL has spacial and magnitude dependent distortions in its proper motion system. They are slightly improved by incorporating Gaia observations, but they are not fully removed. Due to the short life expectancy of HSOY, a careful re-reduction of PPMXL is out of question.
This plot shows the the mean errors in proper motion in RA (red) and Dec (blue), in bins of 1 mag:
Since the early epochs are missing in USNO-B1 south of -30 degrees (no early surveys available), the errors in proper motion are much larger there; here is the distribution of errors in RA:
and in Dec:
To illustrate HSOY's coverage, this is a plot of the number of objects per level-6 healpix cell:
Here is a table of minimal, mean, and maximal values of the main HSOY columns:
col | min | avg | max |
raj2000 | 5.684374286825e-07 | 210.993388137 | 359.999993202 |
dej2000 | -89.9928427252 | -9.98338171978 | 89.9901000584 |
e_raepRA | 4.74927e-09 | 9.14502574957e-07 | 2.38159e-05 |
e_deepDE | 6.27509e-09 | 7.75452288327e-07 | 2.36765e-05 |
pmRA | -0.00216075 | -4.43904220127e-07 | 0.00242583 |
pmDE | -0.00245665 | -1.09799220875e-06 | 0.00257913 |
e_pmRA | 1.14448e-08 | 8.34744285904e-07 | 2.68803e-06 |
e_pmDE | 1.13905e-08 | 8.34238460892e-07 | 2.62362e-06 |
epRA | 1975.62 | 2014.8336071 | 2015.0 |
epDE | 1978.95 | 2014.88429072 | 2015.0 |
Jmag | -0.676 | 15.1470283958 | 21.749 |
e_Jmag | 0.013 | 0.0737119978739 | 9.999 |
Hmag | -1.739 | 14.5851051481 | 24.292 |
e_Hmag | 0.0 | 0.0891082665977 | 9.999 |
Kmag | -2.099 | 14.3843849985 | 20.532 |
e_Kmag | 0.0 | 0.102864557141 | 9.999 |
b1mag | 1.6 | 18.6243196919 | 50.0 |
b2mag | 0.014 | 18.7001648827 | 65.38 |
r1mag | -3.159 | 17.3583684551 | 65.47 |
r2mag | 0.024 | 17.710484873 | 62.38 |
imag | 2.171 | 16.704232572 | 64.5 |
nobs | 3 | 5.5826345577950630 | 17 |
gaia_id | 65408 | 4045094535853177834 | 6917528993283204480 |
phot_g_mean_mag | 3.15463 | 17.8191975575 | 28.6129 |
e_phot_g_mean_mag | 1.06456e-05 | 0.00625220915035 | 0.109 |
G magnitudes and their errors are only given where the flux error as given in DR1 is smaller than 10% of the flux. In that case, the flux errors are translated into magnitude errors 1.09*flux_err/flux.
(1) Duplicates: PPMXL contains many non-matched stars, i.e., two objects where only one should be present. Where the proper motion computed for these stars is roughly correct, these non-matched pairs end up in HSOY as well. All will be matched to the same Gaia DR1 object, which makes them behave rather odd kinematically (they "collide" at the epoch of Gaia). Such cases are marked with a 1 in the clone column. Clearly, astrometry has to be used with great care for these objects.
(2) Conversely, quite a few PPMXL objects match several Gaia DR1 objects. Since the true autocorrelation of Gaia DR1 (and several following releases) has a sharp drop at 2 arcsec for technical reasons, these objects do typically not correspond to multiple star systems but reflect match failures in the construction of Gaia DR1. In HSOY, such cases are marked with a non-NULL comp (which may remind you of component; in some rare cases, that association could actually match reality). This is a plot of (sum(comp)+sum(clone))/n in level-6 healpix cells, which is a good indicator of the severity of the problems with (1) and (2). The grid pattern represents the overlap areas in the surveys that entered into USNO-B, where problem (1) is particularly severe:
(3) As discussed in 2010AJ....139.2440R, PPMXL inherited from USNO-B about 2.5e7 spurious objects with high proper motions, mostly on the edges of plates, where pairs were matched that should not have been matched. Most of these objects did not hit Gaia DR1 objects when moved to J2015. Thus, HSOY only contains about 2.5e6 objects faster than 150 mas/yr (2.5e5 on the northern sky). Comparing this with the expectation of less than 1e5 from 2005AJ....129.1483L in the northern sky, it is clear that there still are many spurious high-PM objects in HSOY. To aid in discarding invalid high-PM objects, we matched PPMXL with SuperCOSMOS (cf. 2001MNRAS.326.1279H), which an independent extraction of the plates USNO-B is based on. Objects failing to match at J2000 received a 1 in HSOY's no_sc column. Note that for technical reasons, False in no_sc is encoded as NULL. Therefore, to filter out probably spurious objects, write WHERE no_sc IS NULL.
This purges another factor of two in bad high-PM objects all-sky (to 1.4e6). On the northern sky, the result is particularly pronounced, where only 1.7e5 objects with PM>150 mas/yr are left, well within a factor of two of the gold standard set by LSPM.
Here are comparisons of the distributions of total proper motions in HSOY for all (blue) and no_sc IS NULL (red) objects. Top or left is for the total catalog, bottom or right just the northern sky.
To get an idea of where the obvious problem on the southern sky comes from, see this density map of stars faster than 150 mas/yr in HEALPixes of order 6, plotted in galactic coordinates. Only objects for which all of no_sc, comp, and clone are NULL are shown. Note that the scale on the aux axis is logarithmic:
Essentially, in areas so crowded that almost any movement of a star will hit another (within our match criteria) there will be many spurious high-pm stars, in particular when there are many spurious sources to begin with (plate borders). In sufficient distance from the bulge and the Magellanic clouds, high proper motions in HSOY should be fairly reliable when filtering out the suspicious (no_sc, clone, comp) objects.
(4) HSOY inherits the USNO photometry in B, R, and I. It has many known issues (including, but not limited to, ridiculous values like 65.47 shown in the table above). Do not lightly use b1mag, b2mag, r1mag, r2mag, and imag, as many of them are invalid.
(5) At the bright end, HSOY is severely incomplete. This reflects the corresponding incompleteness of Gaia DR1.
The primary key of HSOY is the tuple (ipix,comp). The suggested reference to a HSOY object is "HSOY <ipix>.0" when comp is NULL, and "HSOY <ipix>.<comp>" otherwise.
If you want to cite HSOY, please see our citation advice.
You can access this service using:
0.51661 3.35107 eV
2000 2000
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 |
gaia_id | Source Id | Unique source identifier | N/A | meta.id |
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 | Search radius | Search radius in arcminutes | N/A | N/A |
ipix | Id | The PPMXL object identifier, which in turn is the q3c ipix of the original USNO-B object; for HSOY, only (ipix, comp) is a unique identifier (primary key). The recommended identifier form is 'HSOY ipix.comp', where comp=0 for NULL comps. This is what the SCS generates. | N/A | meta.id.cross |
Kmag | m_K_s | K_s selected default magnitude from 2MASS | mag | phot.mag;em.IR.K |
maxrec | Match limit | Maximum number of records returned. Pass 0 to retrieve service parameters. | N/A | N/A |
phot_g_mean_mag | m_G | Mean magnitude in the G band from Gaia DR1. Magnitudes for which err_flux/flux>0.1 have been dropped. | mag | phot.mag;em.opt;stat.mean |
RA | Alpha (ICRS) | Right Ascension (ICRS decimal) | deg | pos.eq.ra |
responseformat | Output Format | File format requested for output. | N/A | meta.code.mime |
SR | Search Radius | Search radius | deg | N/A |
verb | Verbosity | Exhaustiveness of column selection. VERB=1 only returns the most important columns, VERB=2 selects the columns deemed useful to the average user, VERB=3 returns a table with all available columns. | N/A | 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 |
---|---|---|---|---|
_r | Dist. | Distance to cone center | deg | pos.distance |
clone | Clone | If 1, more than one PPMXL object matched to this Gaia object (i.e.: proper motion is probably wrong, any apparent duplicity is probably spurious). This is normally due to failed matching of objects from different plates in USNO-B. Note cl | N/A | meta.code.qual |
dej2000 | Dec | Declination J2000.0, epoch 2000.0 | deg | pos.eq.dec;meta.main |
e_deepDE | E_deepde | Mean error in Dec at mean epoch | deg | stat.error;pos.eq.dec;meta.main |
e_Jmag | Err(m_J) | J total magnitude uncertainty | mag | stat.error;phot.mag;em.IR.J |
e_phot_g_mean_mag | Err. m_G | Estimated error in Gaia G-band magnitude. This is estimated as 1.09*err_flux/flux which is good as a symmetric 1 σ-error of the magnitude to at least within a few percent when err_flux/flux is smaller than 0.1, as it is for the HSOY objects. | s**-1 | stat.error;phot.mag;em.opt.V |
e_pmDE | Err. PM(Dec) | Mean error in pmDE | deg/yr | stat.error;pos.pm;pos.eq.dec |
e_pmRA | Err. PM(RA) | Mean error in pmRA*cos(delta) | deg/yr | stat.error;pos.pm;pos.eq.ra |
e_raepRA | E_raepra | Mean error in RA*cos(delta) at mean epoch | deg | stat.error;pos.eq.ra;meta.main |
gaia_id | Source Id | Unique source identifier Note id | N/A | meta.id |
Hmag | m_H | H selected default magnitude from 2MASS | mag | phot.mag;em.IR.H |
hsoyid | HSOY Id | HSOY identifier (ipix plus comp from original table) | N/A | meta.id;meta.main |
Jmag | m_J | J selected default magnitude from 2MASS | mag | phot.mag;em.IR.J |
Kmag | m_K_s | K_s selected default magnitude from 2MASS | mag | phot.mag;em.IR.K |
phot_g_mean_mag | m_G | Mean magnitude in the G band from Gaia DR1. Magnitudes for which err_flux/flux>0.1 have been dropped. | mag | phot.mag;em.opt;stat.mean |
pmDE | PM(Dec) | Proper Motion in Dec | deg/yr | pos.pm;pos.eq.dec |
pmRA | PM(RA) | Proper Motion in RA*cos(delta) | deg/yr | pos.pm;pos.eq.ra |
raj2000 | RA | Right Ascension J2000.0, epoch 2000.0 | deg | pos.eq.ra;meta.main |
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 |
---|---|---|---|---|---|
hsoyid | HSOY Id | HSOY identifier (ipix plus comp from original table) | N/A | meta.id;meta.main | 1 |
gaia_id | Source Id | Unique source identifier Note id | N/A | meta.id | 1 |
raj2000 | RA | Right Ascension J2000.0, epoch 2000.0 | deg | pos.eq.ra;meta.main | 1 |
dej2000 | Dec | Declination J2000.0, epoch 2000.0 | deg | pos.eq.dec;meta.main | 1 |
pmRA | PM(RA) | Proper Motion in RA*cos(delta) | deg/yr | pos.pm;pos.eq.ra | 1 |
pmDE | PM(Dec) | Proper Motion in Dec | deg/yr | pos.pm;pos.eq.dec | 1 |
_r | Dist. | Distance to cone center | deg | pos.distance | 10 |
clone | Clone | If 1, more than one PPMXL object matched to this Gaia object (i.e.: proper motion is probably wrong, any apparent duplicity is probably spurious). This is normally due to failed matching of objects from different plates in USNO-B. Note cl | N/A | meta.code.qual | 15 |
e_phot_g_mean_mag | Err. m_G | Estimated error in Gaia G-band magnitude. This is estimated as 1.09*err_flux/flux which is good as a symmetric 1 σ-error of the magnitude to at least within a few percent when err_flux/flux is smaller than 0.1, as it is for the HSOY objects. | s**-1 | stat.error;phot.mag;em.opt.V | 15 |
e_raepRA | E_raepra | Mean error in RA*cos(delta) at mean epoch | deg | stat.error;pos.eq.ra;meta.main | 15 |
e_deepDE | E_deepde | Mean error in Dec at mean epoch | deg | stat.error;pos.eq.dec;meta.main | 15 |
e_pmRA | Err. PM(RA) | Mean error in pmRA*cos(delta) | deg/yr | stat.error;pos.pm;pos.eq.ra | 15 |
e_pmDE | Err. PM(Dec) | Mean error in pmDE | deg/yr | stat.error;pos.pm;pos.eq.dec | 15 |
Jmag | m_J | J selected default magnitude from 2MASS | mag | phot.mag;em.IR.J | 15 |
Hmag | m_H | H selected default magnitude from 2MASS | mag | phot.mag;em.IR.H | 15 |
Kmag | m_K_s | K_s selected default magnitude from 2MASS | mag | phot.mag;em.IR.K | 15 |
phot_g_mean_mag | m_G | Mean magnitude in the G band from Gaia DR1. Magnitudes for which err_flux/flux>0.1 have been dropped. | mag | phot.mag;em.opt;stat.mean | 20 |
e_Jmag | Err(m_J) | J total magnitude uncertainty | mag | stat.error;phot.mag;em.IR.J | 20 |
epRA | Epra | Mean Epoch (RA) | yr | time.epoch;pos.eq.ra | 25 |
epDE | Epde | Mean Epoch (Dec) | yr | time.epoch;pos.eq.dec | 25 |
e_Hmag | Err(m_H) | H total magnitude uncertainty | mag | stat.error;phot.mag;em.IR.H | 25 |
e_Kmag | Err(m_K_s) | K_s total magnitude uncertainty | mag | stat.error;phot.mag;em.IR.K | 25 |
b1mag | USNO mag (B1) | B mag from USNO-B, first epoch Note 1 | mag | phot.mag;em.opt.B | 25 |
b2mag | USNO mag (B2) | B mag from USNO-B, second epoch Note 1 | mag | phot.mag;em.opt.B | 25 |
r1mag | USNO mag (R1) | R mag from USNO-B, first epoch Note 1 | mag | phot.mag;em.opt.R | 25 |
r2mag | USNO mag (R2) | R mag from USNO-B, second epoch Note 1 | mag | phot.mag;em.opt.R | 25 |
imag | USNO mag (I) | I mag from USNO-B Note 1 | mag | phot.mag;em.opt.I | 25 |
nobs | #Obs | Number of observations contributing to this column (always nobs(ppmxl)+1) | N/A | meta.number;obs | 25 |
magSurveys | USNO Mag src. | Surveys the USNO-B magnitudes are taken from Note 2 | N/A | meta.code | 28 |
VOResource XML (that's something exclusively for VO nerds)
Magnitudes from USNO-B should be used with care. Photometric calibration may be severely off for some plates.
For objects from PPMX (bit 1 set in flags), these magnitudes have a special meaning as per the following table:
PPMXL column | PPMX column | PPMX content |
---|---|---|
b1mag | Cmag | Catalogue magnitude from source |
b2mag | Bmag | Johnson B magnitude |
r1mag | Rmag | calc. Ru magnitude from source |
r2mag | N/A | always None |
imag | Vmag | Johnson V magnitude |
See also the PPMX table info .
magSurveys is built by concatenating the digits assigned to the surveys for b1mag, b2mag, r1mag, r2mag, and imag (in this sequence). The digits are those of given in Note h to Table 3 in 2003AJ....125..984M, except we do not distinguish POSS-II N and SERC-I as a part of POSS-I-N (i.e., both 7 and 9 are 7 here).
From this field, you can also see which of the surveys contributing to USNO-B had positions for the object.
During the construction of USNO-B, numerous observations were not matched properly. As a result, at least 10% of USNO-B objects are spurious. Most of these carried over into PPMXL. Since many of these objects have completely errneous proper motions, much fewer will be in HSOY. However, they are present, and they are characterised by multiple PPMXL objects being matched to one Gaia object. Since PPMXL's resolution is much worse than Gaia's, these will almost always be spurious; also, since the Gaia position is fixed in both solutions, their paths will cross fairly near to J2015.0.
For the contents of Gaia DR1 (and hence TGAS), which does not include Solar System objects, the source ID consists of a 64-bit integer, least significant bit = 1 and most significant bit = 64, comprising:
This means that the HEALpix index level 12 of a given source is contained in the most significant bits. HEALpix index of 12 and lower levels can thus be retrieved as follows: