David's Astronomy Pages (Solar System) Minor Planet 37655 Illapa

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	37655 Illapa
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	Observations - 2003-08-13 (early morning)
	Observations - 2003-08-09 (early morning)
	Observations - 2003-08-03 (late evening)
	Observations - 2003-08-03 (early morning)

37655 Illapa

37655 Illapa or 1994 PM was discovered 1994-08-01 by C. S. Shoemaker and E. M. Shoemaker at Palomar.  It is a Potentially Hazardous Asteroid (PHA) and has a diameter of c. 1km, 

Illapa was the thunder or weather god of the Incas. Hailing rain down from the celestial river (the Milky Way), Illapa fed the empire. According to legend, he would crack his sister's water jug with a slingshot, reverberating the echoes of thunder as water spilled forth from the sky, showering the parched lands below.
 (From the Dictionary of Minor Planet Names)

In August 2003, Illapa made a close approach to Earth (approaching to 0.02504AU on 2003-08-16).  Observations of Illapa were made on 3 nights between 2003-08-03 and 2003-08-13 when it was still in the northern sky and sufficiently high (>20 deg altitude) to permit telescope observations from my observatory.

It had been hoped to submit observations to the A.L.P.O. NEO Campaign Illapa (37655) as very little is known about this PHA.

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Results 

Measured magnitude and motion of Illapa are tabulated below and compared against Predicted values (predicted values from TheSky based on MPCORP data of 2003-07-28)

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Observations 2003-08-13

37655 Illapa marked by cross-hairs. Note how its image is streaked, due to its movement  during the 60 sec CCD exposure.  (minor planet moving at 15.4 arc sec/minute)

CCD image,  60 sec exposures (unfiltered) 2003-08-13  02:35h UT (#51234) 11.4 x 5.9 arc mins

Composite montage, showing rapid (15.4 arc min/hour) movement of Illapa  through starfield in Aquarius over 2 hours (click on image to see at full size 0.4 MB)

CCD images,  60 sec exposures (unfiltered) 2003-08-13  01:02 to 03:04h UT (#51152, 173, 199, 224, 242, 260) 11.4 x 7.6 arc mins

Light Curve for 37655 Illapa, generated from 104 CCD Images   taken over a period of 2 hours ( Light Curve display in Excel). The light curve records an apparent 0.6  mag variation  (unfiltered mag range of +13.2 to +13.8),  Data quality isn't sufficient to be confident in  assessing a rotational period for the minor planet.  This was mainly due  to the object's comparatively low S/N ratio (S/N of 4) associated with its low magnitude  in comparison with a bright moonlight background sky. (2003-08-13  01:01 to  03:03h UT (#51122- 51260)

See earlier images of Illapa on 2003-08-08 when movement was recorded at 3.87 arc min per hour and Illapa on 2003-08-03 when movement was recorded as 1.25 arc min per hour and 

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Observations 2003-08-09

Illapa  (moving into Aquarius) Composite image recorded over 2 hours  showing Illapa's rapid movement of 3.87 arc min per hour due to its close distance to Earth, 0.117 AU from Earth

CCD image,  108 x 60 sec exposures (summed) 2003-08-09  01:12 to 03:19h UT (#50049-152) 11.4 x 7.6 arc mins

Animated sequence of CCD Images showing movement of Illapa (37655)  click on image below to run animation

60 sec exposures 2003-08-09  01:08 to 03:16h UT (#50048-150)

Light curve for 37655 Illapa

Light Curve for 37655 Illapa, generated from 101 CCD Images  (60 sec exposures)  taken over a period of 2 hours. The light curve records an apparent +/- 0.2 mag variation about an average mag of +15.33. Possible trough at 02:15 to 02:20h UT, but unconfirmed due to time gap in images. Data quality isn't sufficient to be confident in  assessing a rotational period for the minor planet.   2003-08-09  01:08 to 03:16h UT (#50048-152)

See images of Illapa on 2003-08-03 when movement was recorded as 1.25 arc min per hour. 

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Observations 2003-08-03 (late)

Illapa (37655)   calibrated unfiltered magnitude +16.8  (vs catalog mag of +15.8)

CCD image (60 sec exposure) 2003-08-03  23:07 h UT (#48069)  11.4 x 7.6 arc mins

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Observations 2003-08-03 (early)

Illapa (37655)  (crossing through Ophiuchus)

Animated sequence of CCD images,   60 sec exposures at approx 6 minute intervals over 40 minute period. Minor planet recorded as moving across celestial  background at 1.25 arc min per hour. S/N of around 4 was no lower than on 2003-08-13 even though the minor planet was  around  3 magnitudes brighter, this was because the sky background  on 2003-08-03 was considerably darker (due to absence of moon) Average measured unfiltered magnitude +16.70 2003-08-03  01:20 to 02:00 h UT (#47162 and others)  8.5 x 5.7 arc mins

Light Curve for 37655 Illapa, generated from 28 CCD Images  (60 sec exposures)  taken over a period of 40 minutes. The light curve records a 0.5 range in apparent magnitude (+16.4  to +16.9).  Magnitudes in first part of period show more scatter due to brighter sky background (ie more noise), however overall interpretation is that the data shows a real drop in magnitude at c. 01:50 to 01:55 h UT against a overall trend of increasing brightness (related to approach to Earth) 2003-08-03  01:20 to 02:00h UT (#47164-191)

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