J/A+A/561/A37 Prediction of stellar occultations 2012.5-2014 (Camargo+, 2014)
Candidate stellar occultations by Centaurs and TNOs up to 2014.
Camargo J.I.B., Vieira-Martins, R., Assafin M., Braga-Ribas F., Sicardy B.,
Desmars J., Andrei A.H., Benedetti-Rossi G., Dias-Oliveira A.
<Astron. Astrophys. 561, A37 (2014)>
=2014A&A...561A..37C 2014A&A...561A..37C
ADC_Keywords: Positional data ; Occultations ; Minor planets
Keywords: astrometry - occultations - Kuiper belt: general
Abstract:
The prediction tables of stellar occultations by 5 Centaurs and 34
TNOs (referred simply as TNOs hereafter) for the period 2012.5-2014
were built to support the investigation of the physical properties of
(8405) Asbolus, (24835) 1995 SM55, (10199) Chariklo, (26375) 1999 DE9,
(47171) 1999 TC36, (38628) Huya, (54598) Bienor, (55565) 2002 AW197,
(55576) Amycus, (83982) Crantor, (119951) 2002 KX14, (307261) 2002
MS4, (84522) 2002 TC302, (55637) 2002 UX25, (55638) 2002 VE95,
(119979) 2002 WC19, (120132) 2003 FY128, (174567) 2003 MW12, (120178)
2003 OP32, 2003 UZ413, (84922) 2003 VS2, (90568) 2004 GV9, 2004 NT33,
(175113) 2004 PF115, (120347) Salacia, (120348) 2004 TY364, (144897)
2004 UX10, 2005 CC79 (2011 FX62), (303775) 2005 QU182, (145451) 2005
RM43, (145452) 2005 RN43, (145453) 2005 RR43, (202421) 2005 UQ513,
2007 JH43, (278361) 2007 JJ43, (225088) 2007 OR10, (229762) 2007
UK126, 2008 OG19, and 2010 EK139 for this period. These objects are
important to understand the structure, origin, and evolution of the
outer solar system. Our goal was to derive precise predictions. With
this aim, we constructed astrometric star catalogues in the UCAC4
system covering their sky paths. For that, we carried out during
2011-2013 an observational program at the ESO2p2/WFI instrument
covering the sky path of these 39 TNOs for the period 2012.5-2014. We
made the astrometry of 550 GB of images with the Platform for
Reduction of Astronomical Images Automatically (PRAIA). By relatively
simple astrometric techniques, we treated the overlapping observations
and derived a field distortion pattern for the WFI mosaic of CCDs to
within 50mas precision. The catalogue star positions were obtained in
the UCAC4 frame with uncertainties of 40mas for stars up to magnitude
completeness (about R=19). New stellar proper motions were also
determined with 2MASS and the USNO B1.0 catalogue positions as first
epoch. The catalogues for all TNOs contain in all more than 12.4
million entries, covering the sky paths of the objects with 30 arcmin
width. The magnitude completeness is about R=19 with a limit about
R=21. Ephemeris offsets with about 10mas to 100mas precision were
applied for each TNO orbit to improve the predictions. They were
obtained during 2011-2013 from a parallel observational campaign
carried out with telescope diameters from 0.6m to 2.2m.
The 7343 candidate stars listed in the prediction tables were searched
using a proximity radius of 650mas with the geocentric apparent orbit
(corrected by ephemeris offsets) of the body considered. This radius
is a little more than seven times the apparent radius of a body with
Pluto's size (50mas) plus the apparent Earth radius (285 mas) as
projected in the sky plane at 31AU (about the Pluto-Earth distance
for 2008-2015). No threshold in R magnitude was used in the search for
candidates, as relatively faint R objects may turn out to be bright
infrared stars, perfect targets for the SOFIA observatory and for
ground-based instruments well equipped with J, H, or K band detectors
(J, H, and K magnitudes are promptly available in the tables if the
star belongs to the 2MASS). Besides, events may be also favoured by
slow shadow speeds of less than 20km/s. Also, no constraint on a
geographic place was applied, as in principle SOFIA observations can
be done from any sub-solar point on Earth. Events in daylight at
sub-planet point were not excluded either, as they could yet be
observable in the dark, right above the horizon, from places near the
Earth terminator. We furnish here prediction tables for future and
also for past stellar occultations covering the sky paths between
2012.5-2014. The importance of predictions for occultations still to
come is obvious. But the predictions of past occultations are also
useful for at least three reasons. First, they can be used by anyone
as reference for ongoing fittings of light curves of recent past
observed events. Second, they serve to derive ephemeris drifts by
comparing expected and observed central instants and C/A values.
Finally, they can be used as an external check for the accuracy and
precision of our prediction tables.
In all, for R=19 stars (catalogue magnitude completeness) and 40mas
errors in the WFI positions, we may assume a bulk error of about 80mas
for C/A, dominated by the ephemeris offsets errors of about 70mas. For
about 40AU, this implies a shadow path uncertainty over the Earth
of the order of 2300km. If the ephemeris offsets can be well
determined to within 30mas precision, then a bulk error of 50mas in
C/A can be achieved, leading to a precision of about 1400km for the
WFI occultation path predictions. Thus, the probability of actually
observing the occultation is not as high as hoped, but not
despairingly small, especially if the event occurs above a dense,
populated region in terms of astronomers, including amateurs, with
access to telescopes.
Description:
Each prediction table contains the date and instant of stellar
occultation (UTC), the ICRS (loosely J2000) star coordinates at the
event date (that is, corrected by proper motion), the ICRS (J2000)
geocentric right ascension and declination of the TNO at the
occultation, the closest apparent geocentric distance between star and
body, the position angle of the shadow across the Earth (clockwise,
zero at North), the velocity in km/s, the distance to the Earth (AU),
longitude of the sub-solar point, local solar time, ephemerides
offsets in (RA, DEC) for the central instant (see JPL ephemeris
version in Table 5 of the paper), the catalogue proper motion, the
catalogue and multiplicity flags, the estimated star catalogue
position errors, the proper motions and the magnitudes R*, J*, H* and
K*. Magnitudes are normalized to a reference shadow velocity v of
20km/s (the typical shadow velocity of a body at Pluto's distance at
opposition). Mag_normalized=mag+2.5log10(v/20). These normalized
magnitudes may bring forward faint stars involved in slow events, thus
allowing for longer integration time, and consequently reasonably good
signal-to-noise ratios (SNRs) without loss of spatial resolution in
diameter measurements and in probing atmosphere altitudes in the light
curves. This situation is further favored as the brightness of TNOs
are usually smaller than that of the stars. In all, the overall
contribution to the total recorded flux must be evaluated and a case
by case estimation of the SNR must be done for those candidates.
The prediction tables are divided by body and year, with entries in
chronological order. The reference ephemerides used are listed in
Table 5 of the paper. Besides star positions, the ICRS (J2000)
geocentric right ascension and declination of the TNO at the
occultation are also given (they are corrected by ephemeris offsets).
This makes it easy for the reader to evaluate his/her own updates on
the star position or on the ephemeris offsets of the TNOs. Notice that
some tables present zero entries. This is not in error and only means
that for some TNOs and years no occultation is foreseen. Also notice
that it is possible that some few predictions are associated to false
detections (artifacts).
Abstract for additional star catalogs:
The catalogues of star positions and proper motions for 5 Centaurs and
34 TNOs (referred simply as TNOs hereafter) covering their sky paths
for 2012.5-2014 were built to support precise astrometric predictions
of stellar occultations by (8405) Asbolus, (24835) 1995 SM55, (10199)
Chariklo, (26375) 1999 DE9, (47171) 1999 TC36, (38628) Huya, (54598)
Bienor, (55565) 2002 AW197, (55576) Amycus, (83982) Crantor, (119951)
2002 KX14, (307261) 2002 MS4, (84522) 2002 TC302, (55637) 2002 UX25,
(55638) 2002 VE95, (119979) 2002 WC19, (120132) 2003 FY128, (174567)
2003 MW12, (120178) 2003 OP32, 2003 UZ413, (84922) 2003 VS2, (90568)
2004 GV9, 2004 NT33, (175113) 2004 PF115, (120347) Salacia, (120348)
2004 TY364, (144897) 2004 UX10, 2005 CC79 (2011 FX62), (303775) 2005
QU182, (145451) 2005 RM43, (145452) 2005 RN43, (145453) 2005 RR43,
(202421) 2005 UQ513, 2007 JH43, (278361) 2007 JJ43, (225088) 2007
OR10, (229762) 2007 UK126, 2008 OG19, and 2010 EK139 for this period.
For that, we carried out during 2011-2013 an observational program at
the ESO2p2/WFI instrument covering their 2012.5-2014 sky paths. We
made the astrometry of 550GB of images with the Platform for Reduction
of Astronomical Images Automatically (PRAIA). By relatively simple
astrometric techniques, we treated the overlapping observations and
derived a field distortion pattern for the WFI mosaic of CCDs to
within 50mas precision. Positions were obtained in the UCAC4 frame
with uncertainties of 40mas for stars up to the magnitude
completeness (about R=19). New stellar proper motions were also
determined with 2MASS and the USNO B1.0 catalogue positions as first
epoch. Astrometric catalogues with proper motions were produced for
each TNO, containing more than 12.4 million stars covering the sky
paths with 30 arcmin width. The magnitude completeness is about R=19
with a limit about R=21. We highlight the usefulness of these
catalogues as a reference frame for star/body astrometric follow-up
before and after future stellar occultations involving these TNOs. In
this way, the redetermination of the ephemeris of these bodies and of
the position of star candidates for occultations can be enhanced.
Besides, the catalogues also furnish useful photometric information
for field and candidate stars in the preparation of campaigns and flux
calibrations of observed light curves.
Description for additional star catalogs:
Each catalogue consists of (RA, DEC) star positions in the ICRS
(loosely J2000) at mean epoch of observation, proper motions, and
observed R magnitudes. The mean epoch of observation is given as
Julian Date (UTC). The position error at mean epoch of observation and
the uncertainty in the observed magnitude are also furnished. Whatever
the catalogue, more than 90% of the stars are flagged "f0" (good
quality for astrometry, see Table 3 in the paper and references
therein for more details). To a given TNO, three catalogues are given:
one from 2012.5 to the end of 2012, one to the year 2013, and one to
the year 2014.
The uncertainties in position are a combination of the fitting
uncertainty and the standard error from the variance-covariance matrix
of the least-squares reduction that translated each (x,y) coordinate
on the WFI CCDs into right ascension and declination in the ICRS.
Proper motions were computed using the 2MASS as first epoch. If it was
not a 2MASS star, the USNOB1.0 catalog was used instead. If it was
neither a 2MASS nor a USNO B1.0 star, no proper motion was computed.
The second epoch position came from the WFI astrometry. For UCAC4
stars, proper motions were directly extracted from that catalog.
Uncertainties in proper motions are given as 99.999 in this version of
the catalogues. The observations were made with a broad-band R filter
(ESO#844 with lambdacentral=651.725nm and deltalambda=162.184nm at
FWHM). The magnitudes were derived from PSF photometry, but since they
were calibrated in the UCAC4 system, magnitude zero-point errors up to
0.3 might be expected for R>17.
For each TNO, we give separate catalogues labelled per year. Each year
corresponds to the observed sky path. For some TNOs, there are small
gaps without catalogue stars between the years, corresponding to sky
regions where, as seen from Earth, the Sun is too close to the TNO
direction at date (angle Sun-observer-target smaller than 30deg). The
catalogue entries are ordered by increasing right ascension.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 84 117 List of objects with catalog star positions sky
path and prediction stellar occultations
catal/* . 117 Individual files of catalog star positions sky path
tables/* . 117 Individual files for prediction stellar occultations
--------------------------------------------------------------------------------
See also:
J/A+A/541/A142 : Prediction of stellar occultations 2008-2015 (Assafin+, 2012)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.1 yr Year Year of occultation
9- 18 A10 --- Object Object name
22- 38 A17 --- CatFile Name of the file with catalog star positions
sky path, in "catal" subdirectory
40- 46 I7 --- Nc Number of stars in CatFile
48- 53 F6.2 Mibyte Sc Size of CatFile (in 10242 bytes)
56- 72 A17 --- TabFile Name of the file with prediction stellar
occultations, in "tables" subdirectory
74- 77 I4 --- Nt Number of occultations in TabFile
79- 84 I6 byte St Size of TabFile
--------------------------------------------------------------------------------
Byte-by-byte Description of file: catal/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (ICRS) at mean epoch
4- 5 I2 min RAm Right ascension (ICRS) at mean epoch
7- 13 F7.4 s RAs Right ascension (ICRS) at mean epoch
16 A1 --- DE- Declination sign (ICRS) at mean epoch
17- 18 I2 deg DEd Declination (ICRS) at mean epoch
20- 21 I2 arcmin DEm Declination (ICRS) at mean epoch
23- 28 F6.3 arcsec DEs Declination (ICRS) at mean epoch
33- 37 F5.3 arcsec e_RAs Right ascension uncertainty (arcsec*CosDE)
40- 44 F5.3 arcsec e_DEs Declination uncertainty (arcsec)
47- 62 F16.8 d JD Julian Date (UTC)
66- 71 F6.3 arcsec/yr pmRA ?=99.999 Proper motion (ICRS) in
right ascension (pmRA*cosDE) (1)
74- 79 F6.3 arcsec/yr pmDE ?=99.999 Proper motion (ICRS) in
declination (1)
82- 87 F6.3 arcsec/yr e_pmRA [99.999] Uncertainty in pmRA (2)
90- 95 F6.3 arcsec/yr e_pmDE [99.999] Uncertainty in pmDE (2)
97-102 F6.3 mag Rmag Observed R magnitude
105-109 F5.3 mag e_Rmag Uncertainty in observed R magnitude
--------------------------------------------------------------------------------
Note (1): 99.999 indicates that the proper motion was not calculated.
Note (2): Always 99.999 in these catalogues.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tables/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 5 I4 yr App.Y UTC instant at closest approach (year)
7- 8 I2 "month" App.M UTC instant at closest approach (month)
10- 11 I2 d App.D UTC instant at closest approach (day)
14- 15 I2 h App.h UTC instant at closest approach (hours)
17- 18 I2 min App.m UTC instant at closest approach (minutes)
20- 22 F3.0 s App.s UTC instant at closest approach (seconds)
26- 27 I2 h RAh Right ascension (J2000) of star at epoch
29- 30 I2 min RAm Right ascension (J2000) of star at epoch
32- 38 F7.4 s RAs Right ascension (J2000) of star at epoch
40 A1 --- DE- Declination sign (J2000) of star at epoch
41- 42 I2 deg DEd Declination (J2000) of star at epoch
44- 45 I2 arcmin DEm Declination (J2000) of star at epoch
48- 53 F6.3 arcsec DEs Declination (J2000) of star at epoch
57- 58 I2 h RAoh TNO geocentric right ascension (J2000)
at occultation
60- 61 I2 min RAom TNO geocentric right ascension (J2000)
at occultation
63- 69 F7.4 s RAos TNO geocentric right ascension (J2000)
at occultation
71 A1 --- DEo- TNO declination sign (J2000) at occultation
72- 73 I2 deg DEod TNO declination (J2000) at occultation
75- 76 I2 arcmin DEom TNO declination (J2000) at occultation
79- 84 F6.3 arcsec DEos TNO declination (J2000) at occultation
88- 92 F5.3 arcsec Sep Minimum Separation at closest approach (CA)
95-100 F6.2 deg PA Position angle (PA) at closest approach (1)
102-108 F7.2 km/s Vshad Occultation shadow velocity (2)
110-115 F6.2 AU Dist Apparent geocentric distance at occultation
117-120 F4.1 mag Rmag Normalized magnitude (apparent) in R band
122-125 F4.1 mag Jmag Normalized magnitude (apparent) in J band (3)
127-130 F4.1 mag Hmag Normalized magnitude (apparent) in H band (3)
132-135 F4.1 mag Kmag Normalized magnitude (apparent) in K band (3)
139-142 F4.0 deg Long Longitude of the sub-solar point at occultation
144-145 I2 h LST.h Local solar time at closest approach (hours)
147-148 I2 min LST.m Local solar time at closest approach (minutes)
152-158 F7.1 mas oRA Right ascension ephemeris offset correction
161-167 F7.1 mas oDE Declination ephemeris offset correction
169-170 A2 --- f_pm Star proper motion flag (4)
172-173 A2 --- f_cat Catalogue cross-identification flag (5)
175 I1 --- f_Pos Astrometric multiplicity flag (6)
177-180 I4 mas e_RAs Right ascension error at catalogue mean epoch (7)
182-185 I4 mas e_DEs Declination error at catalogue mean epoch (7)
187-190 I4 mas/yr pmRA Proper motion in Right Ascension (RA*cosDE) (8)
192-195 I4 mas/yr pmDE Proper motion in Declination (8)
--------------------------------------------------------------------------------
Note (1): This is the position angle of the body with respect to the star at
closest approach; PA is zero when the body is north of the star and is
counted clockwise.
Note (2): This is the occultation shadow velocity across the Earth at the
apparent geocentric distance of the body; it has a positive/negative sign
for prograde/retrograde velocities, that is, when the TNO's geocentric right
ascension is respectively increasing/decreasing.
Note (3): J, H or K magnitudes marked "50.0" mean no infrared magnitudes
available; this means that it is not a 2MASS star.
Note (4): Star has proper motion? If yes, flag = "ok", otherwise flag = "no".
Note (5): flags as follows:
uc = UCAC4 star
2m = 2MASS star
fs = field star (not a UCAC4 or 2MASS catalogue star)
Note (6): Astrometric multiplicity flags range from 0 to 6 as follows:
0 = final WFI mosaic star position ok; all contributing individual CCD
positions were within 0.2arcsec from each other after the final WFI
mosaic solutions; no nearby individual CCD position was identified
within 1.5arcsec of the final catalogue star position, indicating good
astrometry
1 = a number of individual CCD positions was identified within 1.5arcsec of
each other; more than one of these individual positions was labeled as
a UCAC4 star; the final catalogue position assigned for this star came
from the average over these individual CCD positions labeled as UCAC4;
the same flag is assigned if it refers to the 2MASS catalogue (one can
distinguish between both cases looking at the catalogue flag)
2 = a number of individual CCD positions was identified within 1.5arcsec of
each other; but only one single of these positions was labeled
UCAC4/2MASS; this single position was assigned as the final catalogue
star position (the catalogue flag indicates which catalogue is
involved - UCAC4 or 2MASS)
3 = some contributing individual CCD positions were within 0.2arcsec from
each other after the final WFI mosaic solutions, but the resulting
positions were nearby others within 1.5arcsec; none of these positions
were labeled UCAC4 or 2MASS; here, the final catalogue star position
assigned for this star came from the entry with highest number
(N not equal to 1) of individual position contributions from the WFI
mosaic solution
4 = same situation as in flag "3", but more than one entry presented the
same highest number of individual position contributions; in this case,
the final catalogue star position assigned for this star came from the
single entry with least (x,y) measured errors
5 = same situation as in flag "4", but more than one entry presented the same
best (x,y) measurement errors; in this case, the final catalogue star
position assigned for this star came from the single entry with
brightest R magnitude
6 = same situation as in flag "5", but more than one entry presented the
same brightest R magnitudes; in this case, the final catalogue star
position assigned for this star came from the average over all detected
multiple entries
Note (7): Error values marked "9999" mean no estimated errors; this regards to
astrometric flagged positions or to positions from one observation.
Note (8): proper motion values marked "9999" mean no computed proper motions;
this is because no first epoch position counterpart could be found in
the 2MASS or USNO B1.0 catalogues.
--------------------------------------------------------------------------------
Acknowledgements:
Julio Camargo, camargo(at)on.br
(End) Julio Camargo [ON/MCTI, Brazil], Patricia Vannier [CDS] 06-Dec-2013