International Occultation Timing Association
Lunar Occultations of LB-1 (= X198794) in 2019 and 2020
World maps below text
Lunar occultations of LB-1, including in s.e. USA, Mexico, Caribbean, Canary Is. soon, Dec. 13, 4h UT

Occultation observers have not thought much about 11.4-mag. X198794, only about 8' from 6.4-mag. 6 Geminorum and 0.8 deg. from 3rd-mag. eta Geminorum (Propus) before now. But recently, Chinese astronomers have claimed that LB-1 is orbiting an incredibly massive black hole, some 70 times the solar mass, and LB-1 is this star, also known as UCAC2 39817449 at J2000 RA 06h 11m 49.08s, Dec +22 deg. 49' 32.7". The object is currently undergoing a series of lunar occultations that I have computed with Occult 4. Steve Messner has posted the maps of the regions of visibility of the occultations at https://occultationpages.com/events/XZ198794k.html and I list the remaining events in the series below. Since the Moon tomorrow night will be nearly full and the star is mag. 11.4, it will not be observable by normal occultation recording systems. There is debate about the mass of the black hole, as the assumptions based on the brightness/evolution of LB-1 (a 9 solar mass B-type star) and its radial velocity changes, imply a distance almost twice that determined from the Gaia-measured parallax. The Gaia result is likely right, which will mean a significantly less massive black hole. As far as I know, LB-1 has only been observed at visual wavelengths, and the black hole (or its accretion disk) has not been directly observed at any wavelength. Perhaps one of the objects could be detected by X-ray, gamma ray, or radio observations? If so, then tomorrow night’s occultation could result in new knowledge. But maybe the later occultations, occurring around first or last quarter, or during crescent phases, will allow observation at visual wavelengths with large telescopes; if two at different locations (so with different event position angles) could record the star, then if the black hole accretion disk might be detected after the LB-1 B-type star disappears (or before it reappears, during waning phases), that would allow determination of the separation and P.A. of the objects, which combined with the spectroscopic orbit, would allow an independent direct measurement of the distance.

We wanted to post predictions of the December 13th LB-1 occultation for hundreds of locations, but IOTA’s Occult-4 software won’t allow such “multi-site” calculations for such a visually “unobservable” event. However, Occult-4 can be used to compute the predicted times and circumstances for a specific place (for example, at Miami, Florida, the star will disappear at 3:14:26 UT on the Moon’s sunlit side at PA (position angle) 66 deg., alt. 51 deg., az. 85 deg., and will reappear at 4:34:36 UT on the Moon’s thin dark crescent, PA 268, alt. 69 deg., az. 93 deg. If you have Occult 4 on your Windows computer (you can download it for free at http://occultations.org/observing/software/occult/ - instructions for its use are also there), you can compute your own predictions (or I can compute predictions for you, if serious observations are planned and you can’t compute yourself). For calculating LB-1 lunar occultations, to override the observability limits, you need to set a high “Mag limit adjustment” (on the top left part of the page for computing predictions for single sites) to a high value, select “10” from the pull-down menu. This will generate a huge list of predictions, as LB-1 is in the Milky Way. After you generate the list, click on “with Prediction” in the upper left corner and then click on the “Save” icon. That will save the list to a plain text file that you can open with Notepad and then search for “X198794”, the program’s designation (in the expanded USNO “XZ” Zodiacal catalog) for LB-1.


2019 Dec. 13, 4h UT: Moon almost full, waning
Mexico, s.e. USA, Central America, Caribbean
N. limit central Texas, New England, s. Iberia
S. limit Panama, n. Venezuela

2020 Jan. 9, 14h UT: Moon almost full, waxing
s.e. Asia, China, s.&central Japan, n.&central Philippines, Hawaii? (low)
N. limit w. & n. China, N. Korea, n. Japan
S. limit Sumatra, s. Philippines

2020 Feb. 6, 0h UT: Moon gibbuous, waxing
n.e. USA, Iberia, Canary Is., n.w. Arica
in daylight, Mexico, Caribbean
N. limit New York, Nova Scotia, Newfoundland, n. Iberia, n. Egypt
S. limit n.e. Venezuela, s.w. coast of n.w. Africa

2020 Mar. 4, 10h UT: Moon near first quarter, slightly gibbuous
Japan (dusk), Hawaii
in daylight, India, China
N. limit s.e. Siberia (Kamchatka), Aleutians
S. limit west-central Pacific Ocean

2020 Mar. 31, 17h UT: Moon near first quarter, fat crescent
n. central Europe, w. & central Russia, n.w. India (low);
in daylight, n.e. N. America, UK, n.w. Europe
N. limit Arctic, n. central Siberia
S. limit n. Italy (twilight), Armenia, Afghanistan, s. Pakistan

2020 Apr. 27, 23h UT: Moon thin waxing crescent
Greenland, Iceland, Ireland, UK, Scandinavia (low);
in daylight, Alaska, n. Canada
N. limit (none, above N. Pole)
S. limit n. Atlantic, near Azores

2020 May 25, 4h UT: Almost new moon, very thin waxing crescent
s.e. Alaska, n. Canada
in daylight, n. Scandinavia, w. Russia, n. Siberia, most of Alaska
N. limit (none, above N. Pole)
S. limit near Seattle (low); daylight w. & n. Siberia, s.w. Alaska

2020 June 21, 11h UT: New moon, no night visibility
in daylight, n.&e. Canada, n.e. USA, Greenland, Svalbard, Siberia
N. limit (none, above N. Pole)
S. limit daylight New England, Canadian Atlantic Provinces, n. Norway, Chita

2020 July 18, 11h UT: Near new moon, very thin waning crescent
n.w. & s. cen. Siberia (low, in bright dawn twilight)
in daylight, n. & e. Siberia, Greenland
N. limit (none, above N. Pole)
S. limit daylight Sakhalin, Kamchatka, n. Alaska, n. Canada

2020 Aug. 15, 5h UT: Moon thin waning crescent
n. Canada, Greenland, Iceland, Svalbard (low, in bright dawn)
in daylight, n.e. Siberia, n. Alaska
N. limit (none, above N. Pole)
S. limit daylight Iceland, Svalbard, n.e. Siberia

2020 Sep. 11, 14h UT, Moon fat waning crescent
Part of Arctic Ocean (last occultation of the series)
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