Eclipsing binaries in open clusters. III. V621 Per in chi Persei

V621 Persei is a detached eclipsing binary in the open cluster chi Persei which is composed of an early B-type giant star and a main sequence secondary component. From high-resolution spectroscopic observations and radial velocities from the literature, we determine the orbital period to be 25.5 days and the primary velocity semiamplitude to be K = 64.5 +/- 0.4 km/s. No trace of the secondary star has been found in the spectrum. We solve the discovery light curves of this totally-eclipsing binary and find that the surface gravity of the secondary star is log(g_B) = 4.244 +/- 0.054 (cm/s). We compare the absolute masses and radii of the two stars in the mass--radius diagram, for different possible values of the primary surface gravity, to the predictions of stellar models. We find that log(g_A) is approximately 3.55, in agreement with values found from fitting Balmer lines with synthetic profiles. The expected masses of the two stars are 12 Msun and 6 Msun, and the expected radii are 10 Rsun and 3 Rsun. The primary component is near the blue loop stage in its evolution.Comment: Accepted for publication in MNRAS (10 pages, 5 figures

Circumstellar Structure around Evolved Stars in the Cygnus-X Star Formation Region

We present observations of newly discovered 24 micron circumstellar structures detected with the Multiband Imaging Photometer for Spitzer (MIPS) around three evolved stars in the Cygnus-X star forming region. One of the objects, BD+43 3710, has a bipolar nebula, possibly due to an outflow or a torus of material. A second, HBHA 4202-22, a Wolf-Rayet candidate, shows a circular shell of 24 micron emission suggestive of either a limb-brightened shell or disk seen face-on. No diffuse emission was detected around either of these two objects in the Spitzer 3.6-8 micron Infrared Array Camera (IRAC) bands. The third object is the luminous blue variable candidate G79.29+0.46. We resolved the previously known inner ring in all four IRAC bands. The 24 micron emission from the inner ring extends ~1.2 arcmin beyond the shorter wavelength emission, well beyond what can be attributed to the difference in resolutions between MIPS and IRAC. Additionally, we have discovered an outer ring of 24 micron emission, possibly due to an earlier episode of mass loss. For the two shell stars, we present the results of radiative transfer models, constraining the stellar and dust shell parameters. The shells are composed of amorphous carbon grains, plus polycyclic aromatic hydrocarbons in the case of G79.29+0.46. Both G79.29+0.46 and HBHA 4202-22 lie behind the main Cygnus-X cloud. Although G79.29+0.46 may simply be on the far side of the cloud, HBHA 4202-22 is unrelated to the Cygnus-X star formation region.Comment: Accepted by A

The UKIDSS-2MASS Proper Motion Survey I: Ultracool dwarfs from UKIDSS DR4

The UKIRT Infrared Deep Sky Survey (UKIDSS) is the first of a new generation of infrared surveys. Here we combine the data from two UKIDSS components, the Large Area Survey (LAS) and the Galactic Cluster Survey (GCS), with 2MASS data to produce an infrared proper motion survey for low mass stars and brown dwarfs. In total we detect 267 low mass stars and brown dwarfs with significant proper motions. We recover all ten known single L dwarfs and the one known T dwarf above the 2MASS detection limit in our LAS survey area and identify eight additional new candidate L dwarfs. We also find one new candidate L dwarf in our GCS sample. Our sample also contains objects from eleven potential common proper motion binaries. Finally we test our proper motions and find that while the LAS objects have proper motions consistent with absolute proper motions, the GCS stars may have proper motions which are significantly under-estimated. This is due possibly to the bulk motion of some of the local astrometric reference stars used in the proper motion determination.Comment: Accepted for publication in MNRA

Eclipsing binaries in open clusters. II. V453 Cyg in NGC 6871

We derive absolute dimensions of the early B-type detached eclipsing binary V453 Cygni (B0.4 IV + B0.7 IV, P=3.89d), a member of the open cluster NGC 6871. From the analysis of new, high-resolution, spectroscopy and the UBV light curves of Cohen (1974) we find the masses to be 14.36 +/- 0.20 and 11.11 +/- 0.13 Msun, the radii to be 8.55 +/- 0.06 and 5.49 +/- 0.06 Rsun, and the effective temperatures to be 26600 +/- 500 and 25 500 +/- 800 K for the primary and secondary stars, respectively. The surface gravities of 3.731 +/- 0.012 and 4.005 +/- 0.015 indicate that V453 Cyg is reaching the end of its main sequence lifetime. We have determined the apsidal motion period of the system to be 66.4 +/- 1.8 yr using the technique of Lacy (1992) extended to include spectroscopic data as well as times of minimum light, giving a density concentration coefficient of log(k_2) = -2.226 +/- 0.024. Contaminating (third) light has been detected for the first time in the light curve of V453 Cyg; previous analyses without this effect systematically underestimate the ratio of the radii of the two stars. The absolute dimensions of the system have been compared to the stellar evolution models of the Granada, Geneva, Padova and Cambridge groups. All model sets fit the data on V453 Cyg for solar helium and metal abundances and an age of 10.0 +/- 0.2 Myr. The Granada models also agree fully with the observed log(k_2) once general relativistic effects have been accounted for. The Cambridge models with convective core overshooting fit V453 Cyg better than those without. Given this success of the theoretical predictions, we briefly discuss which eclipsing binaries should be studied in order to further challenge the models.Comment: Accepted for publication in MNRAS (14 pages, 5 figures, Fig.4 reduced in size

Schreiben des Herrn Prof.Fr. Argelander an den Herausgeber

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Beobachtungen des 3ten Cometen von 1843 (im Orion) am 5füssigen Fraunhofer der Bonner Sternwarte

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