Occultation event with (4138) Kalchas, event index number 977
Regions able to see the event: SAfrica
Geocentric closest approach at 2025/05/16 16:58:09 UTC
J2000 position of star is 09:55:13.8 +10:54:28
Equinox of date position of star is 09:56:35.2 +10:47:12
Star is 133 degrees from the moon. Moon is 85% illuminated.
Stellar brightness G=16.1, apparent brightess of occulting body is G=15.9
Use an exposure time of 1.20 seconds with the standard RECON-QHY system.
SNR of 4.8 per integration for unocculted signal
Expected flux drop is 45% with SNR of 2.2 for the occulted depth (per occulted point)
Apparent velocity is 11.4 km/sec on the sky relative to the star, or, 10.8 arcsec/hr.
Position angle of asteroid motion is 334.3 degrees
The recommended exposure time corresponds to 13.7 km per image.
The 1-sigma error in the time of the event is 4.0 seconds.
The 1-sigma cross-track error in the shadow position is 26.7 km.
The sky-plane scale is 3794.2 km/arcsec.
Diameter estimates:
55.7 km assuming a 5% albedo, aximum of 4.9 sec for a central chord
22.8 km assuming a 30% albedo, maximum of 2.0 sec for a central chord
Cross-track diameter of 55.7 km used for deployment plan.
Star training set for 4138_Kalchas, (2025/05/16 16:58UT) Object RA Dec mag sep mel Regulus 10:09:43.2 +11:50:32 1.3 3.39 131 PPM 126849 09:52:11.0 +11:43:21 6.5 1.43 135 PPM 126943 09:57:43.5 +10:32:38 8.0 0.37 133 PPM 126939 09:57:27.8 +10:39:58 9.6 0.25 133 PPM 126918 09:56:06.2 +10:58:59 10.1 0.23 133 4138_Kalchas 09:56:35.2 +10:47:12 15.9 133 Positions are for equinox of date
Star training set for 4138_Kalchas, (2025/05/16 16:58UT) Object RA Dec mag sep mel Regulus 10:08:21.9 +11:58:02 1.3 3.39 131 PPM 126849 09:50:49.2 +11:50:32 6.5 1.43 135 PPM 126943 09:56:22.3 +10:39:55 8.0 0.37 133 PPM 126939 09:56:06.5 +10:47:15 9.6 0.25 133 PPM 126918 09:54:44.7 +11:06:14 10.1 0.23 133 4138_Kalchas 09:55:13.8 +10:54:28 15.9 133 Positions are for J2000