36 research outputs found
Identification of red high proper-motion objects in Tycho-2 and 2MASS catalogues using Virtual Observatory tools
Aims: With available Virtual Observatory tools, we looked for new M dwarfs in
the solar neighbourhood and M giants with high tangential velocities. Methods:
From an all-sky cross-match between the optical Tycho-2 and the near-infrared
2MASS catalogues, we selected objects with proper motions >50mas/yr and very
red V-Ks colours. For the most interesting targets, we collected
multi-wavelength photometry, constructed spectral energy distributions,
estimated effective temperatures and surface gravities from fits to atmospheric
models, performed time-series analysis of ASAS V-band light curves, and
assigned spectral types from low-resolution spectroscopy obtained with CAFOS at
the 2.2m Calar Alto telescope. Results: We got a sample of 59 bright red high
proper-motion objects, including fifty red giants, four red dwarfs, and five
objects reported in this work for the first time. The five new stars have
magnitudes V~10.8-11.3mag, reduced proper motions midway between known dwarfs
and giants, near-infrared colours typical of giants, and effective temperatures
Teff~2900-3400K. From our time-series analysis, we discovered a long secondary
period in Ruber 4 and an extremely long primary period in Ruber 6. With the
CAFOS spectra, we confirmed the red giant nature of Ruber 7 and 8, the last of
which seems to be one of the brightest metal-poor M giants ever identified.Comment: Accepted in Astronomy & Astrophysic
Optimal photometry for colour-magnitude diagrams and its application to NGC 2547
We have developed the techniques required to use the optimal photometry
algorithm of Naylor (1998) to create colour-magnitude diagrams with well
defined completeness functions. To achieve this we first demonstrate that the
optimal extraction is insensitive to uncertainties in the star's measured
position. We then show how to correct the optimally extracted fluxes such that
they correspond to those measured in a large aperture, so aperture photometry
of standard stars can be used to place the measurements on a standard system.
The technique simultaneously removes the effects of a position dependent
point-spread function. Finally we develop a method called "ghosting", which
calculates the completeness corrections in the absence of an accurate
description of the point spread function.
We apply these techniques to the young cluster NGC 2547 (=C0809-491), and use
an X-ray selected sample to find an age of 20-35Myr and an intrinsic distance
modulus of 8.00-8.15 magnitudes. We use these isochrones to select members from
our photometric surveys. Our derived luminosity function shows a well defined
Wielen dip, making NGC 2547 the youngest cluster in which such a feature has
been observed. Our derived mass function spans the range 0.1-6Mo and is similar
to that for the field and the older, more massive clusters M35 and the
Pleiades, supporting the idea of a universal initial mass function.Comment: 24 pages, 20 figures, MNRAS accepte
WIYN Open Cluster Study. XXVI. Improved kinematic membership and spectroscopy of IC 2391
[Abridged] Contex. Young open clusters provide important clues to the
interface between the main sequence and pre-main-sequence phases of stellar
evolution. The young and nearby open cluster IC 2391 is well-suited to studies
of these two evolutionary phases. Aims. We establish a bona fide set of cluster
members and then analyze this set in terms of binary frequency, projected
rotational velocities, [Fe/H], and lithium abundance. In the wake of the
Hipparcos distance controversy for the Pleiades, we compare the main-sequence
fitting distance modulus to the Hipparcos mean parallax for IC 2391. Results.
The proper-motion survey covers a 6 times larger sky area than the prior
targeted searches for cluster members in IC 2391. A total of 66 stars are
considered bona fide cluster members down to a mass equivalent to 0.5M_sun. A
quarter of them have been newly identified with many in the F2-K5 spectral
range, which is crucial for a main-sequence fit. We find a mean [Fe/H] value of
+0.06+/-0.06, when a solar abundance of log epsilon (Fe)=7.45 is adopted. The
main sequence fitting yields a distance modulus that is 0.19 mag larger than
that derived from Hipparcos parallaxes; thus this offset nearly has the size of
a similar offset found for the Pleiades. The Li abundance pattern is similar to
the earlier findings and is typical for a 40 Myr old open cluster.Comment: 18 pages, 11 figures, Astronomy & Astrophysics, in pres
Protecting Important Sites for Biodiversity Contributes to Meeting Global Conservation Targets
Protected areas (PAs) are a cornerstone of conservation efforts and now cover nearly 13% of the world's land surface, with the world's governments committed to expand this to 17%. However, as biodiversity continues to decline, the effectiveness of PAs in reducing the extinction risk of species remains largely untested. We analyzed PA coverage and trends in species' extinction risk at globally significant sites for conserving birds (10,993 Important Bird Areas, IBAs) and highly threatened vertebrates and conifers (588 Alliance for Zero Extinction sites, AZEs) (referred to collectively hereafter as ‘important sites’). Species occurring in important sites with greater PA coverage experienced smaller increases in extinction risk over recent decades: the increase was half as large for bird species with>50% of the IBAs at which they occur completely covered by PAs, and a third lower for birds, mammals and amphibians restricted to protected AZEs (compared with unprotected or partially protected sites). Globally, half of the important sites for biodiversity conservation remain unprotected (49% of IBAs, 51% of AZEs). While PA coverage of important sites has increased over time, the proportion of PA area covering important sites, as opposed to less important land, has declined (by 0.45–1.14% annually since 1950 for IBAs and 0.79–1.49% annually for AZEs). Thus, while appropriately located PAs may slow the rate at which species are driven towards extinction, recent PA network expansion has under-represented important sites. We conclude that better targeted expansion of PA networks would help to improve biodiversity trends
Kinematics And
We present a new determination of the luminosities and kinematics of lower main sequence stars in the spectroscopically selected sample of Vyssotsky, covering spectral types from K3 to M5, using Hipparcos parallaxes and proper motions. The stars separate into two kinematically distinct components, which we label `young' and `old' disk. The young component has velocity dispersion (30, 17, 12) km s \Gamma1 in the UVW directions respectively, asymmetric drift of 8 km s \Gamma1 , a marginally significant vertex deviation of 10 deg \Sigma3 deg, and absolute magnitude M V = 10:48 at color (R \Gamma I) Kron = 1:0 mag. The old component has velocity dispersions (56, 34, 31) km s \Gamma1 , asymmetric drift 28 km/s, and absolute magnitude 0:6 mag fainter at the same color. The slope and intrinsic width of the magnitude calibration of each component are also determined. All results are in agreement with previous determinations using groundbased data, but the errors are considerably smaller...