Introduction

Torricelli B is a small impact crater (simple type), 7 km diameter, located in Sinus Asperitatis (lat. 2.6° S, long. 29.1° E). Usually of medium luminosity, in the night of January 29, 1983, with the Moon a day after the full phase (k=0,986), the crater has attracted the attention of the BAA (Br. Astron. Assoc.) lunar section observers: it was very bright, with albedo superior to Aristarco and encircled by a blue-violet halo. The maximum of brightness has been taken place from 20:55 to 22:40 UT. Others alert on Torricelli B have been had in February and March 1983 and May 1985.

The hight brightness of Torricelli B could be caused from a specular reflection of the solar light. In order to verify this hypothesis it is necessary to watch the crater every time the same Sun-Earth-Moon configuration of January 29, 1983 occour. In recent years one first occasion was on February 9, 2001 at 4:53 UT. In this date the watch of the crater has been prevented by cloudy sky. Better fortune has had the watch in the night between March 29-30, 2002, from 20:30 to 00:30 UT, with the Moon little beyond the full phase (k=0,979).

The observation

For the monitor session I used an achromatic refractor (diameter 150 mm, F/8), connected to a CCD video camera black/white (TC398 model). The used technique is for projection: eyepiece 10 mm focal lenght plus a Minus Violet 1 filter. The filter is for the soppression of the secondary spectrum of the refractor. The acquisition of the images has been made using a PC card TV. The monitor session is started visually at 20 UT at 180X, W8 filter, clear sky and seeing III (Antoniadi scale): the crater was of normal aspect.

From 20:36 UT to 00:28 UT, 16 brief videos (sequences of 30 frames), was registered. From 22:20 ato 23 UT the observation was interrupted by a cloud passage. Same thing from 23:45 to 00:10 UT. Between the registration of the videos, the crater was observed visually from the PC monitor: no sensitive increase of brightness was observed.

Results e discussion

Every sequence of 30 images has been centered and mediated in a single image with Iris 3.54, without more elaborations. In order to trace the light curve of the crater the tecnique of relative photometry has been adopted. I had calculated the ratio between the medium ADU (Analo to Digital Unity) value of the area of Torricelli B, with the medium ADU values of three control zones. The control zones are show in Fig.1. The numerical values are reported in Tab.1. In this way we can put in evidence the variations of Torricelli B brightness, regarding the surrounding regions, eliminating the interferences due to changes of atmospheric transparency. The choice of three distinguished zones allows to control the small errors from zones of various sensibility of CCD sensor or deriving to mediate not on the same pixel.

Fig.1. Region of Torricelli B at 00:28 UT of March 30, 2002. In the immage are show the three zones of comparison, used for relative photometry. Very recognizable the Torricelli crater, from the characteristic 8 shape. The crater low on the left is Theophilus, diameter of 100 km. This image is an average of 30 images, deconvolution with Vancittert, Gaussian filter. Elaboration with Iris 3.54.

The light curve is reported in Fig.2. Every point is the average of three points, everyone relative to a control zone. The error bar on every point is 5% of the value. The light curve is rather flat, without peaks that goes beyond the measure uncertainties.

In conclusion, if the increase of brightness has not take place in the moments of clouds transits, Torricelli B does not give origin to visible specular TLP. This fact induce to think that the TLP of January 29, 1983 was not entirely of specular type.

Fig.2. Light curve of Torricelli B, with relative intensity vs time from 20:36 UT of March 29 to 00:28 UT of March 30, 2002. Every point is the average of three measures. The error bar is 5%.

UT	Torricelli B	Ctl1	Ctl2	Ctl3
20:36	458	452	490	468
20:44	401	398	452	424
21:49	416	415	453	426
21:52	295	278	309	334
22:02	316	296	317	332
22:16	391	373	404	415
23:02	386	383	408	403
23:05	370	362	399	404
23:08	359	349	391	406
23:20	363	359	401	397
23:30	361	353	399	400
23:42	361	350	395	403
00:11	341	327	381	376
00:13	375	364	414	410
00:16	408	406	424	431
00:28	349	340	396	379

Tab.1. Medium ADU values for Torricelli B and the three control zones. From these data the curve of Fig.2 is obtained.

Bibliography

Cook, M.C. The strange behaviour of Torricelli B , J. Br. Astron. Assoc. 110, 3, 2000.

Monitoring program of Torricelli promoted from the UAI Moon section: http://www.uai.it/sez_lun/torricelli_eng.htm

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