71 research outputs found
Aqueye optical observations of the Crab Nebula pulsar
We observed the Crab pulsar in October 2008 at the Copernico Telescope in
Asiago - Cima Ekar with the optical photon counter Aqueye (the Asiago Quantum
Eye) which has the best temporal resolution and accuracy ever achieved in the
optical domain (hundreds of picoseconds). Our goal was to perform a detailed
analysis of the optical period and phase drift of the main peak of the Crab
pulsar and compare it with the Jodrell Bank ephemerides. We determined the
position of the main peak using the steepest zero of the cross-correlation
function between the pulsar signal and an accurate optical template. The pulsar
rotational period and period derivative have been measured with great accuracy
using observations covering only a 2 day time interval. The error on the period
is 1.7 ps, limited only by the statistical uncertainty. Both the rotational
frequency and its first derivative are in agreement with those from the Jodrell
Bank radio ephemerides archive. We also found evidence of the optical peak
leading the radio one by ~230 microseconds. The distribution of phase-residuals
of the whole dataset is slightly wider than that of a synthetic signal
generated as a sequence of pulses distributed in time with the probability
proportional to the pulse shape, such as the average count rate and background
level are those of the Crab pulsar observed with Aqueye. The counting
statistics and quality of the data allowed us to determine the pulsar period
and period derivative with great accuracy in 2 days only. The time of arrival
of the optical peak of the Crab pulsar leads the radio one in agreement with
what recently reported in the literature. The distribution of the phase
residuals can be approximated with a Gaussian and is consistent with being
completely caused by photon noise (for the best data sets).Comment: 7 pages, 7 figures. Accepted for publication in Astronomy and
Astrophysic
The optical light curve of the LMC pulsar B0540-69 in 2009
This paper reports a detailed analysis of the optical light curve of PSR
B0540-69, the second brightest pulsar in the visible band, obtained in 2009
(Jan. 18 and 20, and Dec. 14, 15, 16, 18) with the very high speed photon
counting photometer Iqueye mounted at the ESO 3.6-m NTT in La Silla (Chile).
The optical light curve derived by Iqueye shows a double structure in the main
peak, with a raising edge steeper than the trailing edge. The double peak can
be fitted by two Gaussians with the same height and FWHM of 13.3 and 15.5 ms
respectively. Our new values of spin frequencies allow to extend by 3.5 years
the time interval over which a reliable estimate of frequency first and second
derivatives can be performed. A discussion of implications on the braking index
and age of the pulsar is carried out. A value of n = 2.087 +/- 0.007 for the
overall braking index from 1987 to 2009 is derived. The braking index corrected
age is confirmed around 1700 years.Comment: Accepted for publication in MNRA
Primi rilievi morfometrici del rene di colombo (Columba Livia).
Il nefrone negli Uccelli si presenta eterogeneo sia nella grandezza che nella struttura. Fondamentalmente abbiamo due differenti tipi di nefroni, con e senza ansa di Henle; i primi sono del tipo dei mammiferi (M) e danno un'urina più concentrata, i secondi sono di tipo rettiliano (R) e danno un "urina meno concentrata (Dantzler e Braun, 1980). Anche nel nefrone degli Uccelli è presente l'apparato iuxtaglornerulare che si associa alle cellule del mesangio. Comunque nessun altro gruppo di vertCbrati mostra un cosi semplice disegno di ansa capillare (Dantzler; 1985) in contrasto con i capillari che noi troviamo anastomizzati nei Mammiferi (Braun, 1982). I reni sono organi simmetrici, destro (dx) e sinistro (sn), suddivisi in tre lobi, pressocchè uguali, per mezzo di scissure trasversali di varia profondità : craniale, medio e caudale. Il parenchirna è formato da lobuli piriformi, con una parte più ampia apicale detta corticale e una più piccola detta midollare. I nefroni M sono meno numerosi e situati in prossimità midollare, quelli R sono in periferia. Nel presente lavoro sono stati comparati il numero e la grandezza dci glomeruli renali di colombi a diverse età e sono stati sottoposti ad analisi statistiche
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