A Binary Millisecond Pulsar in Globular Cluster NGC6544

We report the detection of a new 3.06 ms binary pulsar in the globular cluster NGC6544 using a Fourier-domain ``acceleration'' search. With an implied companion mass of ~0.01 solar masses and an orbital period of only P_b~1.7 hours, it displays very similar orbital properties to many pulsars which are eclipsed by their companion winds. The orbital period is the second shortest of known binary pulsars after 47 Tuc R. The measured flux density of 1.3 +/- 0.4 mJy at 1332 MHz indicates that the pulsar is almost certainly the known steep-spectrum point source near the core of NGC6544.Comment: Accepted by ApJ Letters on 11 October 2000, 5 page

Das NSG „Alte Elbe bei Bösewig“ : ein neuer Rast- und Sammelplatz des Kranichs

Das 358,75 ha große Naturschutzgebiet „Alte Elbe bei Bösewig“ liegt etwa 20 km südöstlich von Lutherstadt Wittenberg zwischen dem Hochwasserdeich und der Elbe, unmittelbar östlich der Ortschaft Bösewig. Vom Deich bei Bösewig bietet sich ein Blick auf den inmitten von Überflutungsgrünland gelegenen Mäanderbogen der Elbe, der mit seinem Umland aus überwiegend avifaunistischen Gründen zum Naturschutzgebiet erklärt wurde (LAU 1997). Das Gebiet dient als "Mauser-, Übersommerungs-, Rast- und Überwinterungsgebiet" zahlreicher Vogelarten, zu denen auch der Kranich (Grus grus) zählt

Radiation properties of extreme nulling pulsar J1502-5653

We report on radiation properties of extreme nulling pulsar J1502-5653, by analyzing the data acquired from the Parkes 64-m telescope at 1374 MHz. The radio emission from this pulsar exhibits sequences of several tens to several hundreds consecutive burst pulses, separated by null pulses, and the appearance of the emission seems quasi-periodic. The null fraction from the data is estimated to be 93.6%. No emission is detected in the integrated profile of all null pulses. Systematic modulations of pulse intensity and phase are found at the beginning of burst-pulse sequences just after null. The intensity usually rises to a maximum for the first few pulses, then declines exponentially afterwards, and becomes stable after few tens of pulse periods. The peak phase appears at later longitudes for the first pulse, then drifts to earlier longitudes rapidly, and then systematic drifting gradually vanishes while the intensity becomes stable. In this pulsar, the intensity variation and phase modulation of pulses are correlated in a short duration after the emission starts following a null. Observed properties of the pulsar are compared with other nulling pulsars published previously, and the possible explanation for phase modulation is discussed.Comment: 5 pages, 7 figures. Accepted by MNRA

PSR J1829+2456: a relativistic binary pulsar

We report the discovery of a new binary pulsar, PSR J1829+2456, found during a mid-latitude drift-scan survey with the Arecibo telescope. Our initial timing observations show the 41-ms pulsar to be in a 28-hr, slightly eccentric, binary orbit. The advance of periastron, omegadot = 0.28 +/- 0.01 deg/yr is derived from our timing observations spanning 200 days. Assuming that the advance of periastron is purely relativistic and a reasonable range of neutron star masses for PSR J1829+2456 we constrain the companion mass to be between 1.22 Msun and 1.38 Msun, making it likely to be another neutron star. We also place a firm upper limit on the pulsar mass of 1.38 Msun. The expected coalescence time due to gravitational-wave emission is long (~60 Gyr) and this system will not significantly impact upon calculations of merger rates that are relevant to upcoming instruments such as LIGO.Comment: Accepted MNRAS, 5 pages, 3 figure

ShaneAO: wide science spectrum adaptive optics system for the Lick Observatory

A new high-order adaptive optics system is now being commissioned at the Lick Observatory Shane 3-meter telescope in California. This system uses a high return efficiency sodium beacon and a combination of low and high-order deformable mirrors to achieve diffraction-limited imaging over a wide spectrum of infrared science wavelengths covering 0.8 to 2.2 microns. We present the design performance goals and the first on-sky test results. We discuss several innovations that make this system a pathfinder for next generation AO systems. These include a unique woofer-tweeter control that provides full dynamic range correction from tip/tilt to 16 cycles, variable pupil sampling wavefront sensor, new enhanced silver coatings developed at UC Observatories that improve science and LGS throughput, and tight mechanical rigidity that enables a multi-hour diffraction- limited exposure in LGS mode for faint object spectroscopy science.Comment: 11 pages, 10 figures. Presented at SPIE Astronomical Telescopes + Instrumentation conference, paper 9148-7

Beiträge zur aktuellen Flora der Gegend um Havelberg

Der Beitrag umfaßt eigene floristische Beobachtungen aus dem Havelberger Gebiet, überwiegend der Jahre 1989 bis 1999. Fundangaben des Beitrages von BURKART, KUMMER & FISCHER (1995) werden hier nur ausnahmsweise aufgenommen. Über die früheren Verhältnisse des Havelberger Florengebietes sind wir durch viele Publikationen seit JOACHIMI (1794) unterrichtet. Das umfangreichste Material finden wir bei ASCHERSON (1864), WARNSTORF (1879), POTONIE (1882) und ASCHERSON & POTONIE (1885). Der Botanische Verein der Provinz Brandenburg tagte 1911 und 1934 in Havelberg. Von den Ergebnissen der Exkursionen anläßlich der Tagungen liegen Berichte (HOFFMANN 1911, ULBRICH 1934) vor. In den Flußauen von Havel und Elbe ist eine artenreiche Flora erhalten geblieben. Rückgang und Schwund betrifft hier nur eine beschränkte Anzahl von Arten. Als verschwunden gelten z.B. Clematis recta, Hypericum hirsutum (von mir zuletzt 1951 im Mühlenholz beobachtet), Iris sibirica (von mir 1967 noch in großen Mengen am alten Jederitzer Weg zwischen dem Glien und dem Jederitzer Holz beobachtet in der nassen Ausbildungsform der Auwiese [Cnidio-Deschampsietum]), Nymphoides peltata und Peucedanum officinale

On the formation of low-mass black holes in massive binary stars

Recently (Brown \& Bethe 1994) it was suggested that most stars with main sequence mass in the range of about $18 - 30 M_{\odot}$ explode, returning matter to the Galaxy, and then go into low-mass ($\geq 1.5 M_{\odot}$) black holes. Even more massive main-sequence stars would, presumably, chiefly g o into high-mass ($\sim 10 M_{\odot}$) black holes. The Brown-Bethe estimates gave approximately $5 \times {10}^{8}$ low-mass black holes in the Galaxy. A pressing question, which we attempt to answer here, is why, with the possible exception of the compact objects in SN1987A and 4U\,1700--37, none of these have been seen. We address this question in three parts. Firstly, black holes are generally ``seen'' only in binaries, by the accretion of matter from a companion star. High mass black holes are capable of accreting more matter than low-mass black holes, so there is a selection effect favoring them. This, in itself, would not be sufficient to show why low-mass black holes have not been seen, since neutron stars (of nearly the same mass) are seen in abundance. Secondly, and this is our main point, the primary star in a binary ---the first star to evolve--- loses its hydrogen envelope by transfer of matter to the secondary and loss into space, and the resulting ``naked'' helium star evolves differently than a helium core, which is at least initially covered by the hydrogen envelope in a massive main-sequence star. We show that primary stars in binaries can end up as neutron stars even if their initial mass substantially exceeds the mass limit for neutron star formation from single stars ($\sim 18 M_{\odot}$). An example is 4U\,1223--62, in which we suggest that the initial primary mass exceeded $35 M_{\odot}$, yet X-ray pulsationsComment: uuencoded compressed postscript. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm