Information on Service 'Yale/San Juan SPM4 Catalog'

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The SPM4 Catalog contains absolute proper motions, celestial coordinates, and B,V photometry for 103,319,647 stars and galaxies between the south celestial pole and -20 degrees declination. The catalog is roughly complete to V=17.5. It is based on photographic and CCD observations taken with the Yale Southern Observatory's double-astrograph at Cesco Observatory in El Leoncito, Argentina.

For a list of all services and tables belonging to this service's resource, see Information on resource 'Yale/San Juan SPM4 Catalog'

Service Documentation

Observations

The first-epoch survey, taken from 1965 to 1979, was entirely photographic. The second-epoch survey is approximately 1/3 photographic (taken from 1988 to 1998) and 2/3 CCD-based (taken from 2004 through 2008). The survey consists of fields at 5-degree centers in declination and varying separation along right ascension, but always less than or equal to 5 degrees. Since each photographic plate covers a 6.3 x 6.3 degree area of sky, there is significant overlap in the photographic portion of the survey. Also, each field has a pair of blue and yellow passband plates taken (typically) simultaneouly with the double-astrograph. For a small fraction of the fields, plates were repeated within the same "epoch". Each photographic observation consisted of two offset exposures, one 2 hours in duration, the other 2 minutes. Also, an objective wire grating was always used in order to produce measurable grating images for the brighter stars. In this manner, the effective dynamic range of the plates was greatly increased, allowing bright Hipparocos-magnitude stars to be linked to external galaxies on the same plate. A more thorough description of the plate material and the various image systems is given by Girard et al. (1998).

All SPM plates were scanned with the Precision Measuring Machine (PMM) at the US Naval Observatory's Flagstaff Station (NOFS). The raw pixel data were saved and later analyzed at the US Naval Observatory in Washington (USNO), to obtain image centers and photometric indices for all detectable images.

Beginning in 2001, CCD cameras were installed on the double astrograph in order to complete the SPM second-epoch survey. (Photographic plates with the 103 emulsion were no longer being produced.) Two cameras were installed, a 4K x 4K PixelVision (PV) camera (15 micron pixels) in the focal plane of the yellow lens, and an Apogee 1K x 1K (24 micron pixels) camera behind the blue lens. The latter was later replaced by an Apogee Alta 2K x 2K (12 micron pixels) CCD camera. Exposure times were 120-s, reaching the same depth as the first-epoch plates. As with the plates, the objective grating was in place for the CCD observations. A two-fold overlap of frames with the PV's 0.93 x 0.93 degree FOV was initiated for all SPM fields lacking second-epoch plate material. Eventually, when it was found that a single CCD exposure was superior to the multiple first-epoch plate material in terms of astrometric precision, the two-fold coverage was changed to single coverage with the PV frames. The yellow lens' PV data were used for both astrometry and photometry. The blue lens' Apogee data were used only in the photometric reductions.

Construction of the Catalog

The astrometric reductions, for both the photographic and CCD data, made use of an input "master" catalog that was necessary to properly identify the various multiple images (diffraction grating orders and, in the case of the plates, multiple exposures). This master catalog was constructed by combining the following external catalogs in the specified order;

# Source catalog
1 Hipparcos
2 Tycho2
3 UCAC2
4 2MASS psc
5 2MASS xsc (extended sources, largely (but not entirely!) galaxies)
6 LEDA (confirmed galaxies, Paturel et al. 2005, A&A 430, 751)
7 QSO (Veron-Cetty & Veron 2006, A&A 455, 773)

Objects appearing in multiple catalogs were found by positional coincidence and reconciled by adopting the position of the higher ranked one (Hipparocs being considered best). This master input catalog was then used to identify all measurable images within the list of detections in the SPM plate and CCD data. Thus, an object that does not appear in any of these input catalogs, cannot appear in the SPM4 catalog. The completeness of the SPM4 is the product of the completeness of these input catalogs and the magnitude limits and resolving limits (i.e., ability to center crowded/blended images) of the SPM material.

There are 670 SPM field centers at declination -20 degrees and southward. The SPM4 is comprised of 660 of these fields. There are nine -20-deg fields for which first-epoch plates were never taken and one -20-deg field for which the first-epoch plates were mistakenly not measured. Thus, the northern boundary of the SPM4 sky coverage contains a small number of "notches" at which the northernmost stars are at approximately -21.9 degrees instead of -20 degrees.

An input master catalog, as described above, was constructed from cutouts of the external source catalogs for each of the 660 SPM fields included in the SPM4. Within a single field, each object was assigned a "master" ID number that was simply the running number corresponding to the order of that object in the field's cumulative list. Thus, Hipparcos stars would be assigned the lowest numbers, increasing through Tycho2 stars, UCAC2 stars, etc. Combining the three digit field number with the seven digit master catalog number within a field yields a star's overall SPM4 ID number. Since many stars in the substantial overlap of neighboring fields would possess multiple IDs, the ID from the lowest numbered field was adopted as the unique SPM4 identifier.

Astrometric Reductions

All SPM plates were scanned with the PMM at NOFS. The raw pixel data from the scans were stored and sent to USNO for analysis. The existing StarScan pipeline (Zacharias et al. 2008) was heavily modified by USNO staff to accomodate the SPM pixel data. The overall process included a conversion of the PMM transmission values into density values, smoothing the data for the purposes of image detection and background fitting, and then fitting the unsmoothed 2-d density profiles with an azimuthally symmetric exponential function. (Tests using an elliptical exponential function showed no improvement over the azimuthally symmetric one, even for the slightly elongated 1st and 2nd-order diffraction images.) The derived image positions on each of the 884 PMM CCD footprints required to cover an SPM plate were then transformed into a single global coordinate system using information from the overlap regions of adjacent footprints and the laser interferometric metrology of the footprint centers. As the resulting astrometry from all first-epoch SPM plates was included in the construction of the UCAC3 catalog, further discussion of the PMM data analysis can be found in Zacharias et al. (2010). The USNO-derived centers and image parameters for all detections on the SPM plates, both first and second-epoch plates, were then provided to the Yale SPM team for subsequent reduction.

The SPM CCD frames are corrected for bias, dark (in the case of the Apogee frames, dark current is neglible in the PV), and flatfielding. SExtractor is used to identify detections, give aperture photometry, and provide preliminary x,y centers. Final x,y centers are derived by fitting two-dimensional elliptical Gaussian functions to the image intensities. See Casetti-Dinescu et al. (2007) for further details of the astrometric reduction procedures used with the PixelVision camera data.

In general, similar techniques to those used in constructing previous versions of SPM catalogs were used to build the SPM4. (See Girard et al. 1998, Platais et al. 1998, Girard et al. 2004.) Stars for which both the central-order exposure and first-order grating-image pair were measurable were used to derive and correct each plate's magnitude equation individually. Following the procedures developed for the SPM1 and SPM2 catalogs, all extended sources were given magnitude corrections corresponding to their measured magnitude shifted by -0.7.

In the case of the CCD image centers, there were systematic offsets detected between the position of the central image and the mean of the positions of the grating-order pairs. However, these did not follow the behavior expected for magnitude equation (or charge transfer efficiency effects). Therefore, this offset was corrected as such, a simple offset between the image order systems, instead of as a magnitude equation. (See Casetti-Dinescu et al. 2007.)

Measures from all exposures and all grating-image systems were transformed to a single system for each plate and for each CCD frame. The CCD x,y positions were then corrected for a fixed-pattern geometric distortion believed to be linked to the filter. This correction "mask" was built up from residuals of hundreds of frames at different pointings reduced into UCAC2 coordinates. The corrected CCD x,y positions were then transformed onto the system of the UCAC2 to facilitate pasting together the roughly 50 to 100 frames (depending on whether it had two-fold or single coverage) that comprise a 6 deg x 6 deg SPM field. An overlap method is employed to perform this task, using Tycho2 stars as an external reference system to ensure that systematics from the individual overlap solutions do not accumulate. In this manner, an artificial "pseudo-plate" is built up from CCD frames. This pseudo-plate can then be treated the same as a real second-epoch plate.

In previous versions of SPM catalogs, first- and second-epoch plate pairs were combined to yield relative proper motions per plate pair. These were then corrected to absolute proper motions using external galaxies in the case of SPM1 and SPM2, or Hipparcos star proper motions in the case of SPM3. For the SPM4, instead of combining plate pairs, we have decided to construct the best possible position catalogs at first and at second epoch, over the entire coverage area. This is accomplished by dividing the plates into three groups; first-epoch plates, second-epoch plates, and second-epoch pseudo-plates, then combining plate data within each group using a plate-overlap strategy as follows.

Within each of these plate groups, all plates are pushed through the software pipeline that performs the preliminary reductions described above. This pipeline combines multiple images of the same star (short/long exposure and diffraction orders), corrects the positions for magnitude equation, and then models these x,y positions into RA,Dec from a subset of the Tycho2 catalog adjusted to the epoch of the plate. (The subset is roughly half the Tycho2 stars, those of better quality.) The plate model consists of classical 5th-order distortion terms plus a general 3rd-order polynomial. Uncertainties as a function of magnitude are derived from the scatter of stars with multiple images measured on that plate.

With each plate having been reduced into RA,Dec on the system of Tycho2, we then make use of the overlapping areas to make further adjustments of each plate. This is done in an iterative approach as opposed to a simultaneous global solution. The procedure we're using is to

  1. create an "internal+external" reference catalog by doing a weighted average of mutiply-measured stars' RA,Dec and supplementing this with Hipparcos and Tycho2 positions/proper-motions,
  2. model each plate into this ref catalog with a general 3rd-order model plus classical 5th-order distortion, correcting the plate's RA,Decs at the end of the iteration,
  3. examine the differences in positions, obtained before and after this iteration. If it's still subtstantial, go back to step 1/.

The presence of the Hipparcos/Tycho2 stars in the reference catalog prevents errors from the overlap solutions from accumulating and causing a reference system drift. The number of iterations required for convergence was from 5 to 9 for the three plate groups.

When all is done, i.e., after sufficient convergence of the iterative solutions, the weighted-average positions for every object on every plate are derived and adopted as the celestial coordinates of that object, at the weighted mean epoch for that particular star.

This procedure was applied to the first-epoch plates, the second-epoch plates, and the second-epoch pseudo-plates that had been pasted together from the PV CCD frame data. For this last group, a second "pasting" of the CCDs was performed using preliminary proper motions derived from a first iteration to update all CCD data within a single pseudo-plate to the same epoch. Also, for the pseudo-plate regions it was realized that there were some "holes" in the sky coverage from several causes. In areas with single-fold sky coverage, inaccurate telescope pointing led to occasional gaps between adjacent PV frames. Additionally, some frames that had passed a quality check at the telescope were later found to have problems that rendered them unusable. Finally, there were a handful of SPM fields for which the second-epoch plates were also unusable and pseudo-plates created from an incomplete number of CCD frames in these fields were constructed in their place. In order to avoid having holes or cracks in the SPM4 sky coverage for want of second-epoch positions in these cases, it was decided to supplement the pseudo-plate fields with second-epoch positions taken from the master input catalog. The additional stars and galaxies added were those with input catalog V estimates less than 17.5 in most areas, but a cutoff of V=16.5 was used in two galactic plane fields. Of course, in order to appear in the final SPM4 catalog, a corresponding detection and measure of the object in the first-epoch plate material must exist. Objects with proper motions derived in this manner can be identified in the catalog, their values of np and nc, the number of second-epoch plate and CCD measures per object, will both be zero.

When completed, first-epoch positions and second-epoch positions on the system of the ICRS were in hand for all detected objects in the 660 fields. Uncertainties in the positions were derived from the (weighted) scatter of multiply measured stars as a function of magnitude and this empirical relation calculated for each object according to its magnitude estimate.

The positions and uncertainties were then combined to yield proper motions and proper-motion uncertainties in a straightforward manner. While in theory these proper motions should be on the system of the ICRS via Hipparcos and Tycho2, and thus absolute, in practice an additional correction is needed. Examining the measured proper motions of galaxies within each field as well as the differences with Hipparcos proper motions at the bright end, it was apparent that a residual magnitude equation remained in the derived proper motions. It was decided to calculate a final correction to absolute proper motion per field that was linear with magnitude, using the mean magnitude of galaxies and of Hipparcos stars on the field. Such a linear correction was derived for all 660 fields. The actual proper-motion correction applied to each star in the catalog was the weighted mean of the corrections for the three closest field centers to the star, weighted by the inverse distance from the field center squared.

We note that the quoted uncertainties, particularly those of the proper motions, are unexpectedly (and possibly unrealistically) low. This may be due to the use of weightings that are themselves uncertain enough that a single measurement dominates the calculated mean, more so than it should. The uncertainties will be studied further and presented in an upcoming paper (Girard et al. 2010). In the meantime, the proper-motion uncertainties should be used with caution.

Photometric Reductions

The B,V photometry in the SPM4 is extremely heterogeneous. In some cases, it is derived from our blue and visual filtered CCD cameras. In some cases, it is derived from the PMM measures of our first-epoch plates. And in the cases where neither of these are available or reliable, it is propogated from the input master catalog. In this latter group one can find relatively good photometry from Tycho2 or less reliable extrapolations to B and V magnitudes from 2MASS J,H,K. As such, it is difficult to estimate uncertainties for much of the B,V photometry listed. Our magnitude errors are as likely to be caused by spurious radius measures or inapproriate extrapolations as they are by signal to noise considerations. Thus, we do not provide individual uncertainty estimates for the B,V photometry listed. We do, however, indicate the source of the B and V values given, be they CCD-based, plate-based, or input catalog values.

For the purpose of identifying which image orders should be searched for within the list of detections on a plate or CCD, a magnitude estimate of each star in the input master catalog is needed. For Hipparcos and Tycho2 stars, the B_Tycho and V_Tycho values (transformed to the Johnson system) were adopted. For almost all other stars, B and V photometry was not available so an approximate extrapolation was derived based on 2MASS J,H,K. Hipparcos and Tycho2 stars, which have both B,V and 2MASS photometry, were used to calibrate each SPM field with a relation of the form

B-J = b0 + b1*(J-H) + b2*(H-K) + b3*J*(J-H) + b4*J*(H-K)

with a similar function for V-J. These were used to provide an approximate estimate of B and V for stars without Tycho2 photometry. For the small fraction of objects without Tycho2 or 2MASS photometry, the objects were assumed to be faint and arbitrarily assigned the magnitude limit of the plate or CCD on which it was expected to fall. Again, these input master catalog B,V magnitude estimates were primarily to aid in identifying the various image orders detected. Only in the case that there was neither SPM plate-based photometry nor SPM CCD-based photmetry did these estimates find their way to the final catalog.

The PV and Apogee CCD frames of the second-epoch SPM survey were reduced in a standard fashion using aperture photometry with calibration into Tycho2 V and B photometry (corrected to the Johnson system). When available, these CCD-based magnitudes are provided in the SPM4 catalog, superseding the other magnitude estimates.

Photographic photometry based on the parameters of the image model fits of the PMM scan data proved to be problematic. Among the various image model fit parameters derived, the fit radius provided the best (although still poor) correlation with external calibrating photometry. For extended sources, the radius was, of course, inappropriate. For such objects the input master catalog's magnitude estimate was retained instead, (unless there existed CCD-based photometry). Also, there was a large, non-gaussian scatter between the radius measures and calibrating photometry, indicating that at times the radius estimate was simply erroneous. Thus, during the SPM4 plate photometric reduction procedure, a comparison was made between the preliminarily derived (radius-based) magnitude and that from the input master catalog. If these differed by more than one magnitude, it was interpreted as evidence that one or the either was in error. Since we could not know which, a somewhat expedient choice was made: the fainter of the two magnitude values was retained, under the assumption that the steepness of the luminosity function implies that it is more likely that the star is faint. Unfortunately, the only relevant flag that was retained per star was whether or not it had passed through the plate photometry portion of the pipeline, not whether the resulting magnitude estimate was truly plate-based or a retention of the input master catalog value. The photographic photometry was disappointingly poor in any event. Thus, the only truly reliable B,V photometry in the SPM4 catalog is that flagged as being CCD-based, i.e., with ib=3 and/or iv=3.

Acknowledgements

The Southern Proper Motion program is a decades-long endeavor involving the participation of numerous institutions and countless people. The following is a meager attempt at listing those "countless" many who have contributed to the success of the SPM program, culminating with the release of the SPM4 catalog.

The authors are grateful to the National Science Foundation for their substantial support in the form of a series of grants spanning more than two decades, the University of San Juan for extensive logistical and personnel support throughout the course of the survey, the Argentine CONICET for funding of some of the instrumentation, and Yale University for critical financial support during the completion of the SPM program. Also, the program would not have begun were it not for an initial grant from the Ford Foundation, which we also gratefully acknowledge. Finally, we are indebted to our observers who provided the raw material upon which this catalog is based.

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Input Fields

The following fields are available to provide input to the service (with some renderers, some of these fields may be unavailable):

NameTable Head DescriptionUnitUCD
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 Search radius Search radius in arcminutes N/A N/A
i_gal S/G? Galaxy/extended-source flag N/A src.class.starGalaxy
magV V V magnitude mag phot.mag;em.opt.V
MAXREC Match limit Maximum number of records returned. Pass 0 to retrieve service parameters. N/A N/A
RA Alpha (ICRS) Right Ascension (ICRS decimal) deg pos.eq.ra
RESPONSEFORMAT Output Format File format requested for output. N/A meta.code.mime
spmid Id Unique SPM4 id (field number + input catalog line number) N/A meta.id;meta.main
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

Default Output Fields

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.

NameTable Head DescriptionUnitUCD
_r Dist. Distance to cone center deg pos.distance
dej2000 Dec Declination (ICRS, epoch=2000.0) deg pos.eq.dec;meta.main
e_dej2000 Err. Dec Expected uncertainty in Declination at mean epoch deg stat.error;pos.eq.dec;meta.main
e_pmde Err. PM(Dec) Expected uncertainty in proper motion in Declination, at mean epoch. deg/yr stat.error;pos.pm;pos.eq.dec
e_pmra Err. PM(RA) Expected uncertainty in proper motion in RA (mu_alpha*cos(Dec)), at mean epoch deg/yr stat.error;pos.pm;pos.eq.ra
e_raj2000 Err. RA Expected uncertainty in Right Ascension at mean epoch deg stat.error;pos.eq.ra;meta.main
ep1 1st Ep. Weighted mean epoch of first observation yr time.epoch
ep2 2nd Ep. Weighted mean epoch of second observation yr time.epoch
i_cat From Code for the input catalog Note s N/A meta.code
i_gal S/G? Galaxy/extended-source flag Note g N/A src.class.starGalaxy
i_magB src. B source flag for B magnitude N/A meta.flag;phot.mag;em.opt.B
i_magV src. V source flag for V magnitude N/A meta.flag;phot.mag;em.opt.V
magB B B magnitude Note m mag phot.mag;em.opt.B
magH m_H H selected default magnitude from 2MASS mag phot.mag;em.IR.H
magJ m_J J selected default magnitude from 2MASS mag phot.mag;em.IR.J
magK m_K_s K_s selected default magnitude from 2MASS mag phot.mag;em.IR.K
magV V V magnitude Note m mag phot.mag;em.opt.V
meanep Mean Ep. Weighted mean epoch yr time.epoch
nccd2 N(CCD2) Number of 2nd epoch ccd frames used Note c N/A meta.number
nplates1 N(Plates1) Number of 1st epoch plates used N/A meta.number;instr.plate
nplates2 N(Plates2) Number of 2nd epoch plates used N/A meta.number;instr.plate
pmde PM(Dec) Absolute proper motion in Declination deg/yr pos.pm;pos.eq.dec
pmra PM(RA) Absolute proper motion in RA (mu_alpha*cos(Dec)) deg/yr pos.pm;pos.eq.ra
raj2000 RA Right Ascension (ICRS, epoch=2000.0) deg pos.eq.ra;meta.main
spmid Id Unique SPM4 id (field number + input catalog line number) N/A meta.id;meta.main

VOTable Output Fields

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.

NameTable Head DescriptionUnitUCD Verb. Level
spmid Id Unique SPM4 id (field number + input catalog line number) N/A meta.id;meta.main 1
raj2000 RA Right Ascension (ICRS, epoch=2000.0) deg pos.eq.ra;meta.main 1
dej2000 Dec Declination (ICRS, epoch=2000.0) deg pos.eq.dec;meta.main 1
pmra PM(RA) Absolute proper motion in RA (mu_alpha*cos(Dec)) deg/yr pos.pm;pos.eq.ra 9
pmde PM(Dec) Absolute proper motion in Declination deg/yr pos.pm;pos.eq.dec 9
_r Dist. Distance to cone center deg pos.distance 10
e_raj2000 Err. RA Expected uncertainty in Right Ascension at mean epoch deg stat.error;pos.eq.ra;meta.main 15
e_dej2000 Err. Dec Expected uncertainty in Declination at mean epoch deg stat.error;pos.eq.dec;meta.main 15
e_pmra Err. PM(RA) Expected uncertainty in proper motion in RA (mu_alpha*cos(Dec)), at mean epoch deg/yr stat.error;pos.pm;pos.eq.ra 15
e_pmde Err. PM(Dec) Expected uncertainty in proper motion in Declination, at mean epoch. deg/yr stat.error;pos.pm;pos.eq.dec 15
magB B B magnitude Note m mag phot.mag;em.opt.B 15
magV V V magnitude Note m mag phot.mag;em.opt.V 15
meanep Mean Ep. Weighted mean epoch yr time.epoch 15
magJ m_J J selected default magnitude from 2MASS mag phot.mag;em.IR.J 15
magH m_H H selected default magnitude from 2MASS mag phot.mag;em.IR.H 15
magK m_K_s K_s selected default magnitude from 2MASS mag phot.mag;em.IR.K 15
i_magB src. B source flag for B magnitude N/A meta.flag;phot.mag;em.opt.B 25
i_magV src. V source flag for V magnitude N/A meta.flag;phot.mag;em.opt.V 25
ep1 1st Ep. Weighted mean epoch of first observation yr time.epoch 25
ep2 2nd Ep. Weighted mean epoch of second observation yr time.epoch 25
i_gal S/G? Galaxy/extended-source flag Note g N/A src.class.starGalaxy 25
i_cat From Code for the input catalog Note s N/A meta.code 25
nplates1 N(Plates1) Number of 1st epoch plates used N/A meta.number;instr.plate 29
nplates2 N(Plates2) Number of 2nd epoch plates used N/A meta.number;instr.plate 29
nccd2 N(CCD2) Number of 2nd epoch ccd frames used Note c N/A meta.number 29

Copyright, License, Acknowledgements

This data essentially is a mirror of http://www.astro.yale.edu/astrom/spm4cat/spm4.html. If you use it, please reference 2011AJ....142...15G.

VOResource XML (that's something exclusively for VO nerds)

Note c

If the number of CCD frames used in the second epoch is larger than 9, this column still contains 9. Note that if both the number of plates and the number of CCDs for second epoch are zero, the 2nd-epoch position used to calculate the proper motion was adopted from the input source catalog.

Note g
0 no indication the object is non-stellar.
1 the object is a 2MASS extended source.
2 the object is a LEDA confirmed galaxy.
3 the object is from the Veron-Cetty & Veron QSO catalog.
Note m

These flags indicate the source of the magnitude given:

1 magnitude came from the compiled input catalog
2 magnitude was based on 1st-epoch SPM plates
3 magnitude was based on 2nd-epoch SPM CCD observations
Note s

The catalog the input object was taken from is encoded as follows (for objects in multiple catalogs, the first (lowest number) catalog identification is retained):

1 Hipparcos.
2 Tycho-2.
3 UCAC2.
4 the 2MASS point source catalog (psc).
5 the 2MASS extended source catalog (xsc).
6 the LEDA galaxy catalog.
7 the Veron-Cetty & Veron QSO catalog.