Hi Bernd,

Yes, that remark (about Guide automatically correcting this issue)
is correct.

About 96% of UCAC4 stars are matched to a 2MASS source. Given how much
fainter 2MASS goes, you'd really expect it to be closer to 100%, and
it turns out that almost all of the 4% without 2MASS matches are spurious.
(Actually, I don't know of any counterexamples.) So Guide omits them,
rather than have about one star in 25 be completely bogus.

Many programs probably do so as well. There are probably a few using
the FORTRAN source provided by USNO, written before this issue was noticed.
But a lot of programs use the C source code at

http://www.projectpluto.com/ucac4.htm

This code does have an "include doubtful stars" option that will allow
these objects to be extracted. But it defaults to Off, and you'd be
hard pressed to come up with a reason to turn it On. (Except, I admit,
if somebody asks you, "What's going on with 4UC 588-005876?")

-- Bill

On 01/08/2015 02:05 AM, Bernd Klemt bernd.klemt@... [guide-user] wrote:
> Hello Bill,
>
> is the remark of Jean Lecacheux in the last sentence of the forwarded mail
> correct? FYI, this mail describes an occultation of an apparently nonexisting
> star by a minor planet.
>
> Clear skies
> Bernd
>
> ------- Forwarded message follows -------
>
>
> Le Mardi 6 Janvier 2015 19:44 GMT, Tim Haymes <tvh.observatory@...> a
> écrit:
>
>> 2015 Jan 06, 2053UT
>> http://ocultacions.astrosabadell.org/IBEROC/20150106_005876_summary.html
>> The prediction is for a star of mag 12.6, but there is nothing this bright at
>> the position given. I looked in Aladin at 02 27 38 +27 34 38 (J2000) Regards,
>>
>> Tim Haymes
>> http://www.stargazer.me.uk/
>
>
> Hi.
>
> Unfortunately phantom stars can be found in the UCAC4 catalog.
>
> Through the following address
>
> http://vizier.u-strasbg.fr/cgi-bin/VizieR-5?-ref=VIZ54ad00a913d9&-out.add=.&-sour
> ce=I/322A/out&UCAC4===588-005876
> you may verify that 4UC 588-00576 does have a detailed entry in VizieR !
>
> However, despite the claimed 12.6 red magnitude, we remark there is no match with
> the catalogs Tycho, UCAC2, AC2000, AGK2, 2MASS, etc., and moreover no APASS
> photometry. One may find only one (apparent) positive match with the old Lick
> Observatory Northern Proper Motion survey.
>
> In addition the claimed proper motion of the putative star is fast : 71.6
> mas/year in PA= 331.7 degrees.
>
> Only one faint star lies in vicinity of the claimed position (red cross on the
> attached 6'x 6' "Deep Space Survey" picture) : USNO-B1 1175-0040135 (whose
> probable alias is USNO-B1 1175-0040137) = 2MASS 02273874+2734345. Its red
> magnitude is about 18.0.
>
> I remark that if we assume the above 71.6 mas/year proper motion, then the
> claimed 4UC star had a close appulse with USNO-B1 1175-0040137 =
> 2MASS 02273874+2734345 in the year 1949, or with USNO-B1 1175-0040135
> in the year 1965.
>
> So according to me
> 1/ The fake 4UC 588-00576 actually is 2MASS 02273874+2734345 .
> 2/ Its actual proper motion very probably is small.
> 3/ Its reported magnitude 12.6 in the UCAC4 is entirely fanciful.
>
>
> I already wrote in [planoccult] three times during the last three years that when
> we read in the header of any UCAC4-based prediction something like
> " Mv= *** Mp= *** Mr= *** " (i.e. three equal values)
> then a thorough verification of the star from any independent source has to be
> made absolutely.
>
> Otherwise we get a probability
> - about 10 % that the magnitude is false by more than 1.5 unit,
> - perhaps 1 % that the star - and related occultation - does not exist.
>
> J.Lecacheux
>
>
> PS: I remark that my copy of 'Guide 9' displays 4UC 588-005875 and 588-005877
> close to the claimed position, but that there is no trace of the 588-005876
> label, although the 2MASS star is shown. So it seems that some kind of automatic
> corrective already is incorporated in 'Guide'.
>
> ------- End of forwarded message -------
> Bernd Klemt
>
> Sternwarte Herne, MPC code A18
> Herne, Germany
>
> e-mail: info@...
> http://www.sternwarte-herne.de
>
>
>
> ------------------------------------
> Posted by: Bernd Klemt <bernd.klemt@...>
> ------------------------------------
>