43 research outputs found
The clock genes Period 2 and Cryptochrome 2 differentially balance bone formation
Background: Clock genes and their protein products regulate circadian rhythms in mammals but have also been implicated in various physiological processes, including bone formation. Osteoblasts build new mineralized bone whereas osteoclasts degrade it thereby balancing bone formation. To evaluate the contribution of clock components in this process, we investigated mice mutant in clock genes for a bone volume phenotype. Methodology/Principal Findings: We found that Per2Brdm1 mutant mice as well as mice lacking Cry2-/- displayed significantly increased bone volume at 12 weeks of age, when bone turnover is high. Per2Brdm1 mutant mice showed alterations in parameters specific for osteoblasts whereas mice lacking Cry2-/- displayed changes in osteoclast specific parameters. Interestingly, inactivation of both Per2 and Cry2 genes leads to normal bone volume as observed in wild type animals. Importantly, osteoclast parameters affected due to the lack of Cry2, remained at the level seen in the Cry2-/- mutants despite the simultaneous inactivation of Per2. Conclusions/Significance: This indicates that Cry2 and Per2 affect distinct pathways in the regulation of bone volume with Cry2 influencing mostly the osteoclastic cellular component of bone and Per2 acting on osteoblast parameters
The Îł-ray binary LS 5039: mass and orbit constraints from MOST observations
The results of a coordinated space-based photometric and ground-based spectroscopic observing campaign on the enigmatic Îł-ray binary LS 5039 are reported. 16 d of observations from the MOST satellite have been combined with high-resolution optical echelle spectroscopy from the 2.3-m ANU Telescope in Siding Spring, Australia. These observat ions were used to measure the orbital parameters of the binary and to study the properties of stellar wind from the O primary. We found that any broad-band optical photometric variability at the orbital period is below the 2 mmag level, supporting the scenario that the orbital eccentricity of the system is near the 0.24 ± 0.08 value implied by our spectroscopy, which is lower than values previously obtained by other workers. The low amplitude optical variability also implies the component masses are at the higher end of estimates based on the primary's O6.5V((f)) spectral type with a primary mass of âŒ26 Mâ and a mass for the compact star of at least 1.8 Mâ. The mass-loss rate from the O primary was determined to be 3.7 to 4.8 Ă 10â7 Mâ yrâ1
Accurate masses and radii of normal stars: modern results and applications
This paper presents and discusses a critical compilation of accurate,
fundamental determinations of stellar masses and radii. We have identified 95
detached binary systems containing 190 stars (94 eclipsing systems, and alpha
Centauri) that satisfy our criterion that the mass and radius of both stars be
known to 3% or better. To these we add interstellar reddening, effective
temperature, metal abundance, rotational velocity and apsidal motion
determinations when available, and we compute a number of other physical
parameters, notably luminosity and distance. We discuss the use of this
information for testing models of stellar evolution. The amount and quality of
the data also allow us to analyse the tidal evolution of the systems in
considerable depth, testing prescriptions of rotational synchronisation and
orbital circularisation in greater detail than possible before. The new data
also enable us to derive empirical calibrations of M and R for single (post-)
main-sequence stars above 0.6 M(Sun). Simple, polynomial functions of T(eff),
log g and [Fe/H] yield M and R with errors of 6% and 3%, respectively.
Excellent agreement is found with independent determinations for host stars of
transiting extrasolar planets, and good agreement with determinations of M and
R from stellar models as constrained by trigonometric parallaxes and
spectroscopic values of T(eff) and [Fe/H]. Finally, we list a set of 23
interferometric binaries with masses known to better than 3%, but without
fundamental radius determinations (except alpha Aur). We discuss the prospects
for improving these and other stellar parameters in the near future.Comment: 56 pages including figures and tables. To appear in The Astronomy and
Astrophysics Review. Ascii versions of the tables will appear in the online
version of the articl
A Neptune-sized transiting planet closely orbiting a 5â10-million-year-old star
Theories of the formation and early evolution of planetary systems postulate that planets are born in circumstellar disks, and undergo radial migration during and after dissipation of the dust and gas disk from which they formed^1, 2. The precise ages of meteorites indicate that planetesimalsâthe building blocks of planetsâare produced within the first million years of a starâs life^3. Fully formed planets are frequently detected on short orbital periods around mature stars. Some theories suggest that the in situ formation of planets close to their host stars is unlikely and that the existence of such planets is therefore evidence of large-scale migration^4, 5. Other theories posit that planet assembly at small orbital separations may be common^6, 7, 8. Here we report a newly born, transiting planet orbiting its star with a period of 5.4 days. The planet is 50 per cent larger than Neptune, and its mass is less than 3.6 times that of Jupiter (at 99.7 per cent confidence), with a true mass likely to be similar to that of Neptune. The star is 5â10 million years old and has a tenuous dust disk extending outward from about twice the EarthâSun separation, in addition to the fully formed planet located at less than one-twentieth of the EarthâSun separation
Low-mass and sub-stellar eclipsing binaries in stellar clusters
We highlight the importance of eclipsing double-line binaries in our
understanding on star formation and evolution. We review the recent discoveries
of low-mass and sub-stellar eclipsing binaries belonging to star-forming
regions, open clusters, and globular clusters identified by ground-based
surveys and space missions with high-resolution spectroscopic follow-up. These
discoveries provide benchmark systems with known distances, metallicities, and
ages to calibrate masses and radii predicted by state-of-the-art evolutionary
models to a few percent. We report their density and discuss current
limitations on the accuracy of the physical parameters. We discuss future
opportunities and highlight future guidelines to fill gaps in age and
metallicity to improve further our knowledge of low-mass stars and brown
dwarfs.Comment: 30 pages, 5 figures, no table. Review pape
Evolution of Horizontal-Branch Stars in Globular Clusters: The Interesting Case of V79 in M3
A search for variable stars in the globular cluster M3
We describe here the results of a photometric time-sequence survey of the globular cluster M3 (NGC 5272), in a search for contact and detached eclipsing binary stars. We have discovered only one likely eclipsing binary and one SX Phe-type star in spite of monitoring 4077 stars with V < 20.0 and observing 25 blue straggler stars (BSS), The newly identified SX Phe star, V237, shows a light curve with a variable amplitude. Variable V238 shows variability either with a period of 0.49 d or with a period of 0.25 d. On the cluster colour-magnitude diagram, the variable occupies a position a few hundredths of a magnitude to the blue of the base of the red giant branch. V238 is a likely descendant of a binary blue straggler.As a side result we obtained high-quality data for 42 of the previously known RR Lyrae variables, including 33 of Bailey type ab, seven type c and two double-mode pulsators, We used equations that relate the physical propel-ties of RRc stars to their pulsation periods and Fourier parameters in order to derive masses, luminosities, temperatures and helium parameters for five of the RRc stars. We also tested equations that relate the [Fe/H], M-V and temperature of RRab stars to pulsation period and Fourier parameters. We derived [Fe/H]= -1.42 in good agreement with spectroscopic determinations.</p
Ultraviolet Spectroscopy of AB Doradus with the Hubble Space Telescope: Impulsive Flares and Bimodal Profiles of C IV lambda1549 in a Young Star
We observed AB Doradus, a young and active late-type star (K0-K2 IV-V, P = 0.514 days), with the Goddard High Resolution Spectrograph of the post-COSTAR Hubble Space Telescope with time and spectral resolutions of 27 s and 15 km s(-1) respectively (1994 November 14.08-14.30 UT). The wavelength band (1531-1565 Angstrom) included the strong C Iv doublet (1548.202 and 1550.774 Angstrom formed in the transition region at 10(5) K), the chromospheric Si Ir 1533.432 Angstrom line, and the blend of Si I, C I, and Fe It lines at 1561 Angstrom, The mean quiescent C Iv flux state was characterized by F-CIV = (7.80 +/- 0.34) x 10(5) ergs cm(-2) s(-1), close to the saturated value and 100 times the solar one. The line profile (after removing the rotational and instrumental profiles) is bimodal, consisting of two Gaussians, one narrow (FWHM = 70 km s(-1)) and the other broad (FWHM = 330 km s(-1)). This bimodality is probably due to two separate broadening mechanisms and velocity fields at the coronal base. It is possible that transition-region transient events (random multiple velocities), with large surface coverage, give rise to the broadening of the narrow component while true microflaring is responsible for the broad one, as suggested by Wood, Linsky, & Ayres.The transition region was observed to flare frequently with different timescales and magnitudes. The largest impulsive flare seen in the C Iv lambda 1549 emission, at day 14.22, reached in less than 1 minute a peak differential emission measure N-e(2) V (10(4.85)-10(5.15) K)= 10(51.2) cm(-3) and returned exponentially in 5 minutes to the 7 times lower quiescent level. The 3 minute average line profile of the flare was blueshifted(-190 km s(-1)) and broadened (FWHM = 800 km s(-1)). This impulsive flare could have been due to a chromospheric heating and subsequent evaporation by an electron beam, accelerated (by reconnection) at the apex of a coronal loop.</p