934 research outputs found
Detection of the linear radical HC4N in IRC+10216
We report the detection of the linear radical HC4N in the C-rich envelope of
IRC+10216. After HCCN, HC4N is the second member of the allenic chain family
HC_(2n)N observed in space. The column density of HC4N is found to be 1.5
10**12 cm**(-2). The abundance ratio HC2N/HC4N is 9, a factor of two larger
than the decrement observed for the cyanopolyynes HC$_(2n+1)N/HC_(2n+3)N.
Linear HC_4N has a 3-Sigma electronic ground state and is one of the 3
low-energy isomeric forms of this molecule. We have searched for the bent and
ringed HC4N isomers, but could only derive an upper limit to their column
densities of about 3 10**(12) cm**(-2).Comment: Preprint of 10 page
Two dimensionality in quasi one-dimensional cobalt oxides
By means of muon spin rotation and relaxation (SR) techniques, we have
investigated the magnetism of quasi one-dimensional (1D) cobalt oxides
CoO (=Ca, Sr and Ba, =1, 2, 3, 5 and
), in which the 1D CoO chain is surrounded by six equally spaced
chains forming a triangular lattice in the -plane, using polycrystalline
samples, from room temperature down to 1.8 K. For the compounds with =1 - 5,
transverse field SR experiments showed the existence of a magnetic
transition below 100 K. The onset temperature of the transition () was found to decrease with ; from 100 K for =1 to 60 K for
=5. A damped muon spin oscillation was observed only in the sample with
=1 (CaCoO), whereas only a fast relaxation obtained even at 1.8
K in the other three samples. In combination with the results of susceptibility
measurements, this indicates that a two-dimensional short-range
antiferromagnetic (AF) order appears below for all
compounds with =1 - 5; but quasi-static long-range AF order formed only in
CaCoO, below 25 K. For BaCoO (=), as decreased
from 300 K, 1D ferromagnetic (F) order appeared below 53 K, and a sharp 2D AF
transition occurred at 15 K.Comment: 12 pages, 14 figures, and 2 table
A wide area survey for high-redshift massive galaxies. I. Number counts and clustering of BzKs and EROs
We have combined deep BRIz' imaging over 2x940 arcmin^2 fields obtained with
the Suprime-Cam on the Subaru telescope with JKs imaging with the SOFI camera
at the New Technology Telescope to search for high-redshift massive galaxies.
K-band selected galaxies have been identified over an area of ~920 arcmin^2 to
K_Vega=19.2, of which 320 arcmin^2 are complete to K_Vega=20. The BzK selection
technique was used to obtain complete samples of ~500 candidate massive
star-forming galaxies (sBzKs) and ~160 candidate massive, passively-evolving
galaxies (pBzKs), both at 1.4 5 criterion we also
identified ~850 extremely red objects (EROs). The surface density of sBzKs and
pBzKs is found to 1.20+/-0.05 arcmin^{-2} and 0.38+/-0.03 arcmin^{-2},
respectively. Both sBzKs and pBzKs are strongly clustered, at a level at least
comparable to that of EROs, with pBzKs appearing more clustered than sBzKs. We
estimate the reddening, star formation rates (SFRs) and stellar masses (M_*) of
the sBzKs, confirming that to K_Vega~20 median values are M_*~10^{11}M_sun, SFR
190M_sun yr^{-1}, and E(B-V)~0.44. The most massive sBzKs are also the most
actively star-forming, an effect which can be seen as a manifestation of
downsizing at early epochs. The space density of massive pBzKs at z~1.4-2 is
20%+/-7% that of similarly massive early-type galaxies at z~0, and similar to
that of sBzKs of the same mass. We argue that star formation quenching in these
sBzKs will result in nearly doubling the space density of massive early-type
galaxies, thus matching their local density.Comment: 19 pages, 13 figures, accepted by ApJ. While checking the proofs we
became aware of a material mistake of non-trivial scientific relevance. In
the original it was reported that the comoving volume density of passive
BzK-selected galaxies with =1.7 and more massive than 10^{11}M_sun was
45%+/-15% of the local number density of similarly massive early-type
galaxies. This fraction actually turns out to be 20%+/-7%. Section 6.4, point
5 in section 7, and the abstract have been modified accordingl
The Resolved Stellar Populations in NGC 1705
We present HST photometry of the resolved stellar population in the dwarf
irregular galaxy NGC 1705. The galaxy has been observed with both WFPC2 and
NICMOS, and successful images have been obtained in the F555W, F814W, F110W and
F160W bands. The optical fields cover most of the galaxy, while the infrared
field (NIC2) maps only its central regions. The optical photometry provides
\~20000 objects down to m_F555W ~ 29 in the PC field of view and ~ 20000 in the
three WFCs. In the infrared we have been able to resolve ~ 2400 stars down to
m_{F110W}, m_{F160W} ~ 26. A subsample of 1834 stars have been unambiguously
measured in all the four bands. The corresponding color-magnitude diagrams
(CMDs) confirm the existence of an age gradient, showing that NGC 1705 hosts
both young (a few Myr old) and very old (up to 15 Gyr old) stars, with the
former strongly concentrated toward the galactic center and the latter present
everywhere, but much more easily visible in the external regions. The tip of
the red giant branch (TRGB) is clearly visible both in the optical and in the
infrared CMDs and allows us to derive the galaxy distance. Taking into account
the uncertainties related to both the photometry and the TRGB magnitude --
distance relation, we find that the distance modulus of NGC 1705 is
(m-M)_0=28.54 +- 0.26, corresponding to a distance D=5.1 +- 0.6 Mpc.Comment: aastex, 37 pages, 13 (reduced resolution) .ps figures. Accepted by
AJ. Full resolution figures are available upon request to the first autho
Extremely Metal-Poor Stars. VII. The Most Metal-Poor Dwarf, CS 22876-032
We report high-resolution, high-signal-to-noise, observations of the
extremely metal-poor double-lined spectroscopic binary CS 22876-032. The system
has a long period : P = 424.7 0.6 days. It comprises two main sequence
stars having effective temperatures 6300 K and 5600 K, with a ratio of
secondary to primary mass of 0.89 0.04. The metallicity of the system is
[Fe/H] = -3.71 0.11 0.12 (random and systematic errors) -- somewhat
higher than previous estimates. We find [Mg/Fe] = 0.50, typical of values of
less extreme halo material. [Si/Fe], [Ca/Fe], and [Ti/Fe], however, all have
significantly lower values, ~ 0.0-0.1, suggesting that the heavier elements
might have been underproduced relative to Mg in the material from which this
object formed. In the context of the hypothesis that the abundance patterns of
extremely metal-poor stars are driven by individual enrichment events and the
models of Woosley and Weaver (1995), the data for CS 22876-032 are consistent
with its having been enriched by a zero-metallicity supernova of mass 30
M. As the most metal-poor near-main-sequence-turnoff star currently
known, the primary of the system has the potential to strongly constrain the
primordial lithium abundance. We find A(Li) (= log(N(Li)/N(H)) + 12.00) = 2.03
0.07, which is consistent with the finding of Ryan et al. (1999) that for
stars of extremely low metallicity A(Li) is a function of [Fe/H].Comment: 27 pages, 9 figures, accepted for publication in The Astrophysical
Journal, Sept. 1, 2000 issu
Food Storage in Permafrost and Seasonally Frozen Ground in Chukotka and Alaska Communities
Food cellars, otherwise referred to as ice or meat cellars, (lednik in Russian, k’aetyran in Chukchi, siġļuaq in Iñupiaq, and siqlugaq in Yupik) are a natural form of refrigeration in permafrost or seasonally frozen ground used to preserve, age, and ferment foods harvested for subsistence, including marine mammals, birds, fish, and plants. Indigenous peoples throughout the Arctic have constructed cellars in frozen ground for millennia. This paper focuses on cellars in Russian and American coastal and island communities of the Bering Strait, the region otherwise known as Beringia. This area has a unique, culturally rich, and politically dynamic history. Many traditions associated with cellars are threatened in Chukchi communities in Russia because of the impacts of climate change, relocation, dietary changes, and industrial development. However, even with warmer temperatures, cellars still provide a means to age and ferment food stuffs following traditional methods. In cooperation with local stakeholders, we measured internal temperatures of 18 cellars in 13 communities throughout the Bering Strait region and northern Alaska. Though cellars are widely used in permafrost regions, their structure, usage, and maintenance methods differ and exhibit influences of local climates, traditions, and economic activities. Monitoring internal temperatures and recording structural descriptions of cellars is important in the face of climate change to better understand the variety and resilience of living adaptations in different cold regions.Les caves à denrées, aussi connues sous le nom de caves à glace ou de caves à viande (lednik en russe, k’aetyran en tchouktche, siġļuaq en iñupiaq, et siqlugaq en yupik) constituent une forme de réfrigération naturelle dans le pergélisol ou dans le gélisol saisonnier permettant de conserver, de maturer et de fermenter les denrées récoltées à des fins de subsistance, dont les mammifères marins, les oiseaux, les poissons et les plantes. Cela fait des millénaires que les peuples autochtones de l’Arctique construisent des caves dans le gélisol. Cet article porte sur les caves se trouvant dans les localités côtières et insulaires russes et américaines du détroit de Béring, région qui porte également le nom de Béringie. L’histoire de cette région est unique, culturellement riche et politiquement dynamique. De nombreuses traditions liées aux caves des localités tchouktches de la Russie sont menacées en raison des incidences du changement climatique, de la délocalisation, du changement des régimes alimentaires et de l’expansion industrielle. Cependant, malgré les températures plus élevées, les caves constituent toujours un moyen de maturer et de fermenter les denrées alimentaires selon les méthodes traditionnelles. En collaboration avec les parties prenantes de la région, nous avons mesuré les températures internes de 18 caves situées dans 13 localités de la région du détroit de Béring et du nord de l’Alaska. Bien que les caves soient courantes dans les régions de pergélisol, leur structure, leur usage et les méthodes d’entretien diffèrent, et elles sont à l’image des influences des traditions, des activités économiques et des climats locaux. La surveillance des températures internes et l’enregistrement des descriptions structurales des caves revêtent de l’importance à la lumière du changement climatique, car elles permettent de mieux comprendre la variété et la résilience des adaptations de vie dans différentes régions froides.называемые иногда мясными ямами (лéдник по-русски, к’этыран по-чукотски, Siġļuaq или Siqlugaq по-эскимосски), обустроены как в вечномёрзлых породах, так и в сезонноталом слое и являются естественной формой заморозки для сохранения, выдержки и ферментации пищевых продуктов, добытых для пропитания: мясо морских млекопитающих, дичь, рыба, растения и др. Коренные жители Арктики обустраивали хранилища в мерзлоте на протяжении тысячелетий. Данная статья посвящена подземным хранилищам в российских и американских поселениях на берегах Берингова пролива – региона, также называемого Берингией. Эта территория имеет уникальную, богатую культурой и политически динамичную историю. Многие традиции, связанные с хранилищами в поселениях Чукотки, находятся под угрозой исчезновения из-за климатических изменений, миграции жителей, изменений в рационе и промышленного освоения территории. Однако даже при повышении температуры воздуха в хранилищах по-прежнему можно выдерживать и ферментировать пищу традиционными способами. При сотрудничестве с местным населением мы измерили температуры внутреннего воздуха в 18 лéдниках в 13 поселениях в регионе Берингова пролива и на севере Аляски. Несмотря на широкое использование таких хранилищ в криолитозоне, их структура, использование и методы обслуживания различаются под влиянием климатических условий, традиций и особенностей промысла. Мониторинг внутренней температуры воздуха в лéдниках и описание их конструкций важны в контексте изменения климата для лучшего понимания разнообразия и эффективности различных способов адаптации к жизни в холодных регионах
The Unique History of the Globular Cluster Omega Centauri
Using current observational data and simple dynamical modeling, we
demonstrate that Omega Cen is not special among the Galactic globular clusters
in its ability to produce and retain the heavy elements dispersed in the AGB
phase of stellar evolution. The multiple stellar populations observed in Omega
Cen cannot be explained if it had formed as an isolated star cluster. The
formation within a progenitor galaxy of the Milky Way is more likely, although
the unique properties of Omega Cen still remain a mystery.Comment: published version with minor change
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