ABSOLUTE MAGNITUDE - DEVELOPMENTS
MAP Alert #294,
Greetings MAP Observers:
This past week, Gerard Faure and myself have sought to present information on the recent postings to the Minor Planet Mailing List topic "Huge O-C in magnitudes", and their relationship to this program. Gerard has composed a review for readers below. A second MAP Alert with an analysis and future of MAP will follow.
The changes underway will not place "suggested revised H values" out of our reach in the present. But with more advancement in the years to come, these changes will begin to limit the number of researchers who can reach the limits in which useful work can be achieved. Such progress is present in perhaps every
area of amateur research. But perhaps as one door closes, another will open, time will tell here.
Perhaps our MAP members and readers of the
MAP Alerts recently read a thread named "Huge O-C in magnitudes" on
the Minor Planet Mailing List, but for
those who are not on this list, there are some interesting facts in this discussion, but also a big change on the future H magnitudes furnished by the Minor Planet Center.
Following the "discovery" of a high discrepancy of more than 3 magnitudes for the minor planet (135304) 2001 SA249 by Reiner Stoss other examples were given on the MPML notably for many new numbered asteroids – mainly faint – but’ also the case of (1444) Pannonia, well known by the MAP Members.
Gerard also furnished a list of the 30 highest differences of H magnitude found in the years 1996-2006 by the MAP, among the "bright" asteroids followed by the amateurs (below)
1444) Pannonia 2,6 mag Fainter
(1388) Aphrodite 1,6 mag F
(6823) 1988 ED1 1,6 mag F
(44227) 1998 QP14 1,6 mag F
(6911) Nancygreen 1,6 mag F
(1384) Kniertje 1,5 mag F
(5641) Mc Cleese 1,4 mag F
(4440) Tchantches 1,4 mag F
(5749) 1991 FV 1,4 mag F
(881) Athene 1,3 mag F
(5738) Billpickering 1,3 mag F
(5785) Fulton 1,3 mag F
(8021) Walter 1,3 mag F
(4860) Gubbio 1,2 mag F
(10772) 1990 YM 1,2 mag F
(1166) Sakuntala 1,2 mag F
(3873) Roddy 1,1 mag F
(5026) Martes 1,1 mag F
(4483) Petofi 1,1 mag F
(7663) 1994 RX1 1,1 mag F
(2096) Vaino 1,0 mag F
(5404) Uemura 1,0 mag F
(12929) 1999 TZ1 1,0 mag F
(6047) 1991 TB1 1,0 mag F
(870) Manto 0.9 mag Brighter
(1789) Dobrovolsky 0,9 mag B
(1994) Shane 0,9 mag F
(4804) Pasteur 0,9 mag F
(5732) 1988 WC 0,9 mag F
(6619) Kolya 0,9 mag F
As frequently in the past for the MAP on various lists, some sceptic MPML readers reacted and wrote that the causes of the discrepancies of H magnitudes were perhaps the significant magnitude variation associated with rotation, but also with the change of the phase angle or the aspect angle from an opposition to another one.
Gerard answered that "In a personal analysis of all the 2658 lightcurves known on
These results were published in the file "MAP REPORT 1996-2006_ENGLISH.xls" put on the AUDE-MAP Website. In the part "analysis N°4 : Impact of the natural variability of the minor planets" of this file, it was noted : "The natural variability of the asteroids is not a crucial problem for the MAP because :
1) An asteroid doesn't reach its maximum amplitude of light at each opposition, due to the different vision angle of this body from Earth, from an opposition to the next one.
2) When it's the case, they are at the maximum or the minimum just during a short time, one time by entire rotation, the average of the rotation period of the minor planets being about 9 hours.
3) It's only the half-amplitude of light which has a possible impact for the MAP. 90% of the asteroids with known light curves have at most or less than 0.3 magnitude of maximum half-amplitude !
4) For the 10% of asteroids more variable, the maximum half-amplitude of light is problematic only during some oppositions, at the moments of maximums and minimums of light...then in average less than 1 observation made on 6 to 8 !
5) With the computation of the average of all the measures made for an asteroid, the statistical effect reduces or eliminates the impact of measurements made near a maximum or a minimum of light. Then the natural variability of the asteroids has generally only a small repercussion on the MAP objects !"
Despite these facts, the discussion continued, but thanks to the intervention from Alan HARRIS, Senior Research Scientist at the Space Science Institute and expert in the asteroid photometry, our advice lastly was admitted.
Alan HARRIS wrote :
"I recently examined the Light curve Data Base (LCDB), maintained by myself, Warner and Pravec, and can essentially confirm the comments by Gerard
FAURE. My examination of the LCDB is perhaps more critical than his in that I eliminated any results of low reliability or exaggerated claimed light curve amplitude (e.g. from a few obviously discordant observations). I found only ten asteroids which can be confirmed to exhibit, at low phase angle, amplitudes greater than 1.5 magnitudes. Here is a paragraph I wrote, from a paper, in final review for publication in Icarus, commenting on the limits of shape variation of "rubble pile" asteroids:
Examining the Asteroid Light curve Database (LCDB) maintained by Warner et al. (2008), we find, out of more than 3,000 light curve entries, only ten asteroids have observed light curves with confirmed amplitude of variation equal to or exceeding 1.5 magnitudes. The eleventh largest amplitude, (433) Eros at 1.49 magnitudes, has a well measured shape of about 3.0:1 elongation, exactly the limit we find for a non-rotating rubble pile (Eros itself is fairly rapidly rotating, so is not really at its limit). Among the ten with still larger amplitudes, up to a maximum of about 2.0 magnitudes, two are small, super-fast rotators (P < 2.2 h) with some
tensile strength and thus not rubble piles subject to the elongation limit we are discussing; three are quite fast rotators, like Eros, with periods < 7 h and thus able to sustain greater elongation due to the additional centrifugal force sustaining their shape; and four were observed at large solar phase angle, with amplitudes that would likely be less than 1.5, or even 1.2, magnitude at low phase angle, thus are not likely more elongate than the 3:1 limit. The one remaining case is (5247) Krylov, a very slow rotating asteroid (P » 81.5 h) and therefore essentially “non-rotating” as far as centrifugal forces are concerned. Its measured light curve amplitude
is difficult to determine exactly, since it is a non-principal axis rotator (“tumbling”), but appears to be right around 1.5 magnitude at 15°-19° solar phase angle. Thus it is likely no more elongate than Eros and within the 3:1 elongation limit we have calculated.
Thus, even aside from issues of rubble pile or not, only around ten out of 3,000 asteroids with measured light curves have amplitudes exceeding 1.5 magnitudes. I would further add that Jewitt, along with his students Mann (not a man) and Lacerda have found that a set of only several (less than 10) photometric measurements separated in time by more than the presumed but unknown rotation period of an asteroid suffice to pin down the mean magnitude and amplitude of variation to within 0.1 magnitude or so. So I would have to say that light curve variation hardly even enters into the uncertainty budget of an H value derived from estimates of magnitude made from astro metric surveys alone. Yes, some of them really are that bad. Plus, a handful of gross errors, even due to typography or other problems not related to measurement, out of tens of thousands of objects, isn't bad. Both the surveys and the MPC have other priorities, which I respect even if they aren't my own.
This email is very interesting for the MAP, because lastly it has the confirmation by an expert in the domain of the asteroid photometry, that the variability is not a problem for the measure of the H magnitude, when sparse V measures are made, as in the MAP.
Of course, the MAP also his concerned sometimes by an inaccuracy of the measures and the difficulties to join all the measures, but we were more careful than the MPC up to now.
The thread ended with the email from Gareth WILLIAMS, the manager of the MPC, who announced the BIG NEWS which is THE FUTURE UPDATE OF THE H MAGNITUDES BY THE MPC : "..As of earlier this month, we have abandoned use of an official list for H magnitudes for numbered minor planets. The H values will be recomputed whenever new orbits are published, in the same fashion as unnumbered minor planets. As part of the MPC preparation procedure, we publish new orbits for numbered minor planets that are off the prediction from the previous orbit by more than 1 or that have significant arc extensions. The batch of MPCs currently in production has orbits for 4302 previously-numbered objects: " most have newly-computed H values (which in some cases are the same as the already-published values)... Our previous ability to keep the numbered orbits as up to date as for the unnumbered objects has been constrained by an official IAU agreement, which has been widely ignored by other groups."
It is a very good new for the asteroid science and the observers of minor planets, but this is also a MAJOR NEW for the MAP which tried up to now, as Astdys, to obtain rectified H magnitudes for the asteroids with false absolute magnitudes. This new fact induced a thought for the future of the MAP program. This reflection was proceeded by an analysis of the last modifications of H magnitudes by the MPC in its batch of September 17 The results of this analysis and of the thought will be given in a next MAP Alert.
ALPO Minor Planet Section Assistant Coordinator
MAP Alert Homepage
AUDE Web Pages
Gerard Faure (8297 gerardfaure)
MAP Alert #295,
October 01, 2008
Hi to all,
As Lawrence is busy, I send you this new MAP Alert which contains our analysis of the recent revision of the H magnitudes of many numbered asteroids by the MPC, on September 17,2008, for the first time since 1998 !
It's a great new, but it also opens a new period for the MAP, because slowly but surely, the program will reach its end, when all the revised H magnitudes of the "bright" numbered asteroids by the MPC will be accurate (for a fixed G = 0.15 ).
Actually, after the first analysis of the revised H magnitudes, one can say that it's not yet the case !
Below, you will find the results of our first analysis and our first thoughts to also change some things in the MAP data.
1) Analysis of the first modifications of H magnitudes by the MPC :
I used my last updated database of the asteroids N°1 to 189407 known at the end of July 2008 and the data of a MPCORBcr.file of
In 3 big Excel files of Excel 2003, I put the new official H magnitudes of the MPC numbered asteroids and the ancient ones (called "2007" in this email).
I made the comparison of all the new and ancient H magnitudes. After, I searched all the objects with new discrepancies > 0.2 magnitudes and all the MAP objects with their previous averaged discrepancy of H magnitude. I put them together in a single smaller Excel file sent today to you, joined to this MAP Alert.
In this file, I made grey all the objects fainter than V16.6 at the maximum, taking into account the modifications of many H magnitudes by the MPC. These faint asteroids are numerous.
We analyzed the file and found that :
After the N°50000, the asteroids generally are very faint for the amateurs and then there are only few possible comparisons MAP-MPC, exclusively for the numbered NEA.
Among the new H magnitudes concerning the minor planets with a number greater than N°50000, there are mostly corrections for a brighter H magnitude, due to many highly false measures from the SDSS program, as noted in the MPML thread.
Only 5 corrections for a H magnitude > 1.0 mag fainter than those of 2007 were made on asteroids > N°50000. The MPC already corrected in the past the H magnitudes of the unnumbered minor planets before their definitive numbering, notably the NEA for which many have their H magnitude frequently corrected toward the revised H MAP magnitude of this period.
The corrections of H magnitudes by the MPC are not entirely made, as noted by Gareth Williams in this MPML email, because the MPC will modify them only during the corrections of the previous inaccurate orbital elements of the asteroids.
The record of modification of H mag by the MPC in September 2008 was -5,10 magnitudes for (156397) 2001 YK147 with H 2007 = 20,3 and H
The files of "Five brightest V mag" from Warner will need to be made again. Some objects very faint will become visible in the amateur telescopes as the best example of (68000)2000 XM32 : ancient V18,7 max. (H 2007= 17,6) and new H 2008= 15,3 => #H = -2,30 NP => V16.5 maximum
Among the MAP objects, there is no modification of H mag by the MPC, for the objects up to F/0.5 or B/0.5, expect for :
(6153) Hershey H 2007 = 11,5; H 09/2008 = 12,7; # H = 1,20; old M1=F/0.5?; M1 new =B/0.7?
(5208) Royer H 2007 = 11,6; H 09/2008 = 12,5; # H = 0,90; Mc = F/0.3c; M1 new = F/1.2?
On the 457 objects of the MAP, only 4 objects with a difference of H MAP < 1.1 mag have been modified by the MPC, while 10 objects on the 19 with # H MAP > 1.0 mag have been modified !
No MAP object with # H MAP > 1.0 mag seen during a single opposition has been taken in account, but all those published (3 oppositions and more) or with at least 2 observed oppositions have their H mag modified, apart (5641) McCleese may be forgotten. But, for 4 of the 10 objects with a H MAP difference > 1.0 mag, only 4 H mags revised by the MAP correspond to the new H mag of the MPC.
We think that the MPC used our list of objects highly clashing - put on the MPML - to locate the objects, but after the MPC made its H modifications according to the measures of its own internal database. As the MPC never answered to our emails, we shall never have the confirmation, but certainly it was the case. The MAP list was useful !
The MPC seems to have processed by elimination of the very bad photometric measures, but effectively has not yet used a new method more efficient for the obtaining of accurate H magnitudes.
The MAP magnitudes certainly have a small inaccuracy, but for (1444)
2) General strategy :
Actually, we have to continue to do measures because :
1) Nearly 400 MAP objects had not be observed during at least 3 oppositions, then we have no definitive results for them.
2) It's not sure that the modifications from the MPC are good (unidentified false measures or bad color type put on other measures) and it will be interesting to verify the objects concerned by the MPC modifications, notably the new objects concerned by apparent high discrepancies between old and new H magnitudes of the MPC.
3) New conflicting objects may be found among asteroids not yet observed by the MAP.
The best is to keep the MAP database with the official H magnitudes "2007" for the included objects and to compare the evolution of the H MPC magnitudes with regard to our database containing the original H magnitudes. For the next "new" MAP objects, the H magnitude used for the first measure will be the basis for the future.
It would be interesting to obtain from Bernard Guillaud-Saumur new tables 2009 of MAP opposition objects and lists of conjunctions of LONEOS stars with the MAP objects and with MPC objects having a high modification of H magnitude.
One MAP member would follow the changes of H magnitudes by the MPC at least one time by month, at each batch of the MPC, to obtain the historic evolution of the modifications of the H Mags and to permit the connection of eventual old MAP measures with the used H magnitudes of this time.... but who ?
We have to analyze and to do measures with the new method from R. Miles and R.Dymock based on the stellar Catalog CMC14 and the Astrometrica software modified by H.Raab. This work will permit to attract again CCD observers. We hope to do it soon.
3) Future Updates of the MAP Database :
In the MAP Database, I shall add a line by object to put the most recent H of the MPC and the new H difference of the MAP.
Each MAP measure will be computed again with regard to the H MPC 2007 for the old MAP objects, to keep the historic differences of measures and to permit the increase of the accuracy of the MAP measures.
Then the comparison with the new H magnitudes of the MPC will be made during a second calculation made on the averaged H difference 2007, to obtain the updated averaged difference of MAP H magnitude.
When the revised H magnitudes of the MAP will correspond to the MPC magnitudes, at + or - 0,1 or 0,2 mag, then we shall "close" the object and shall consider it "out of the MAP".
If possible, we shall publish on the Minor Planet Bulletin the measures of the objects seen at least during 3 oppositions (and 3 observers, if there will be sufficiently observers) and which will continue to have an interesting discrepancy of magnitude ( # H MAP - H MPC > 0,2 mag ), but also a list of the minor planets for which the MPC and the MAP will obtain the same revised H magnitudes.
4) Observations :
It will be also necessary to know the MPC H magnitude used to the observations and the measures, because the absolute magnitudes of the MPC will continuously change.
Gerard Faure and
ALPO Minor Planet Section Assistant Coordinator
MAP Alert Homepage
AUDE Web Pages
Gerard Faure (8297 gerardfaure)