273 research outputs found
Barium & related stars and their white-dwarf companions I. Giant stars
This paper provides long-period and revised orbits for barium and S stars
adding to previously published ones. The sample of barium stars with strong
anomalies comprise all such stars present in the Lu et al. catalogue. We find
orbital motion for all barium and extrinsic S stars monitored. We obtain the
longest period known so far for a spectroscopic binary involving an S star,
namely 57 Peg with a period of the order of 100 - 500 yr. We present the mass
distribution for the barium stars, which ranges from 1 to 3 Msun, with a tail
extending up to 5 Msun in the case of mild barium stars. This high-mass tail
comprises mostly high-metallicity objects ([Fe/H] >= -0.1). Mass functions are
compatible with WD companions and we derive their mass distribution which
ranges from 0.5 to 1 Msun. Using the initial - final mass relationship
established for field WDs, we derived the distribution of the mass ratio q' =
MAGB,ini / MBa (where MAGB, ini is the WD progenitor initial mass, i.e., the
mass of the system former primary component) which is a proxy for the initial
mass ratio. It appears that the distribution of q' is highly non uniform, and
significantly different for mild and strong barium stars, the latter being
characterized by values mostly in excess of 1.4, whereas mild barium stars
occupy the range 1 - 1.4. We investigate as well the correlation between
abundances, orbital periods, metallicities, and masses (barium star and WD
companion). The 105 orbits of post-mass-transfer systems presented in this
paper pave the way for a comparison with binary-evolution models.Comment: This version 2 is the one accepted by A&A, after language edition.
Paper II about dwarf-Ba and subgiant-CH orbits by Escorza et al. is
arXiv:1904.0409
Hertzsprung-Russell diagram and mass distribution of barium stars
With the availability of parallaxes provided by the Tycho-Gaia Astrometric
Solution, it is possible to construct the Hertzsprung-Russell diagram (HRD) of
barium and related stars with unprecedented accuracy. A direct result from the
derived HRD is that subgiant CH stars occupy the same region as barium dwarfs,
contrary to what their designations imply. By comparing the position of barium
stars in the HRD with STAREVOL evolutionary tracks, it is possible to evaluate
their masses, provided the metallicity is known. We used an average metallicity
[Fe/H] = -0.25 and derived the mass distribution of barium giants. The
distribution peaks around 2.5 Msun with a tail at higher masses up to 4.5 Msun.
This peak is also seen in the mass distribution of a sample of normal K and M
giants used for comparison and is associated with stars located in the red
clump. When we compare these mass distributions, we see a deficit of low-mass
(1 - 2 Msun) barium giants. This is probably because low-mass stars reach large
radii at the tip of the red giant branch, which may have resulted in an early
binary interaction. Among barium giants, the high-mass tail is however
dominated by stars with barium indices of less than unity, based on a visual
inspection of the barium spectral line; that is, these stars have a very
moderate barium line strength. We believe that these stars are not genuine
barium giants, but rather bright giants, or supergiants, where the barium lines
are strengthened because of a positive luminosity effect. Moreover, contrary to
previous claims, we do not see differences between the mass distributions of
mild and strong barium giants.Comment: 14 pages, 17 figure
Lost in Cloud
Cloud computing can reduce cost significantly because businesses can share computing resources. In recent years Small and Medium Businesses (SMB) have used Cloud effectively for cost saving and for sharing IT expenses. With the success of SMBs, many perceive that the larger enterprises ought to move into Cloud environment as well. Government agency s stove-piped environments are being considered as candidates for potential use of Cloud either as an enterprise entity or pockets of small communities. Cloud Computing is the delivery of computing as a service rather than as a product, whereby shared resources, software, and information are provided to computers and other devices as a utility over a network. Underneath the offered services, there exists a modern infrastructure cost of which is often spread across its services or its investors. As NASA is considered as an Enterprise class organization, like other enterprises, a shift has been occurring in perceiving its IT services as candidates for Cloud services. This paper discusses market trends in cloud computing from an enterprise angle and then addresses the topic of Cloud Computing for NASA in two possible forms. First, in the form of a public Cloud to support it as an enterprise, as well as to share it with the commercial and public at large. Second, as a private Cloud wherein the infrastructure is operated solely for NASA, whether managed internally or by a third-party and hosted internally or externally. The paper addresses the strengths and weaknesses of both paradigms of public and private Clouds, in both internally and externally operated settings. The content of the paper is from a NASA perspective but is applicable to any large enterprise with thousands of employees and contractors
Equatorial currents and transports in the upper central Indian Ocean: Annual cycle and interannual variability
The zonal circulation south of Sri Lanka is an important link for the exchange of water between the Bay of Bengal and the Arabian Sea. Results from a first array of three moorings along 80 degrees 30'E north of 4 degrees 10'N from January .1991 to March 1992 were used to investigate the Monsoon Current regime [Schott et al., 1994]. Measurements from a second array of six current meter moorings are presented here. This array was deployed along 80 degrees 30'E between 45'S and 5 degrees N from July 1993 to September 1994 to investigate the annual cycle and interannual variability of the equatorial currents at this longitude. Both sets of moorings contribute to the Indian Ocean current meter array ICM8 of the World Ocean Circulation Experiment. The semiannual equatorial jet (EJ) was showing a large seasonal asymmetry, reaching a monthly mean eastward transport of 35 Sv (1 Sv = 1 x 10(6) m(3) s(-1)) in November 1993, but just 5 Sv in May 1994. The Equatorial Undercurrent (EUC) had a maximum transport of 17 Sv in March to April 1994. Unexpectedly, compared to previous observations and model studies, the EUC was reappearing again in August 1994 at more than 10 Sv transport and was still flowing when the moorings were recovered. In addition, monthly mean ship drifts near the equator are evaluated to support the interpretation of the moored observations. Interannual variability of the EJ in our measurements and ship drift data appears to be related to the variability of the zonal winds and Southern Oscillation Index. The output of a global numerical model (Parallel Ocean Climate Model) driven by the winds for 1993/1994 is used to connect our observations to the larger scale. The model reproduces the EJ asymmetry and shows the existence of the EUC and its reappearance during summer 1994
Barium & related stars and their white-dwarf companions II. Main-sequence and subgiant stars
Barium (Ba) dwarfs and CH subgiants are the less-evolved analogues of Ba and
CH giants. They are F- to G-type main-sequence stars polluted with heavy
elements by a binary companion when the latter was on the Asymptotic Giant
Branch (AGB). This companion is now a white dwarf that in most cases cannot be
directly detected. We present a large systematic study of 60 objects classified
as Ba dwarfs or CH subgiants. Combining radial-velocity measurements from
HERMES and SALT high-resolution spectra with radial-velocity data from CORAVEL
and CORALIE, we determine the orbital parameters of 27 systems. We also derive
their masses by comparing their location in the Hertzsprung-Russell diagram
with evolutionary models. We confirm that Ba dwarfs and CH subgiants are not at
different evolutionary stages and have similar metallicities, despite their
different names. Additionally, Ba giants appear significantly more massive than
their main-sequence analogues. This is likely due to observational biases
against the detection of hotter main-sequence post-mass-transfer objects.
Combining our spectroscopic orbits with the Hipparcos astrometric data, we
derive the orbital inclinations and the mass of the WD companion for four
systems. Since this cannot be done for all systems in our sample yet (but
should be with upcoming Gaia data releases), we also analyse the mass-function
distribution of our binaries. We can model this distribution with very narrow
mass distributions for the two components and random orbital orientation on the
sky. Finally, based on BINSTAR evolutionary models, we suggest that the orbital
evolution of low-mass Ba systems can be affected by a second phase of
interaction along the Red Giant Branch of the Ba star, impacting on the
eccentricities and periods of the giants.Comment: Accepted for publication in A&A on the 5th of April, 201
Does the i-process operate at nearly solar metallicity?
A sample of 895 s-process-rich candidates has been found among the 454180
giant stars surveyed by LAMOST at low spectral resolution (R~1800). In a
previous study, taking advantage of the higher resolution (R~86 000) offered by
the the HERMES-Mercator spectrograph, we performed the re-analysis of 15 among
the brightest stars of this sample. Among these 15 program stars, having
close-to-solar metallicities, 11 showed mild to strong heavy element
overabundances. The nucleosynthesis process(es) at the origin of these
overabundances were however not questioned in our former study. We derive the
abundances in s- and r-process elements of the 15 targets in order to
investigate whether some stars also show an i-process signature, as sometimes
found in their lower metallicity counterparts (namely, the Carbon-Enhanced
Metal-Poor (CEMP)-rs stars). Abundances are derived from the high-resolution
HERMES spectra for Pr, Nd, Sm, and Eu, using the TURBOSPECTRUM radiative
transfer LTE code with MARCS model atmospheres. Using the new classification
scheme proposed in our recent study we find that two stars show overabundances
in both s- and r-process elements well above the level expected from the
Galactic chemical evolution, an analogous situation to the one of CEMP-rs stars
at lower metallicities. We compare the abundances of the most enriched stars
with the nucleosynthetic predictions from the STAREVOL stellar evolutionary
code and find abundances compatible with an i-process occurring in AGB stars.
Despite a larger number of heavy elements to characterize the enrichment
pattern, the limit between CEMP-s and CEMP-rs stars remains fuzzy. It is
however interesting to note that an increasing number of extrinsic stars are
found to have abundances better reproduced by an i-process pattern even at
close-to-solar metallicities.Comment: Accepted for publication in A&A, 9 pages, 9 figures including the two
in appendi
Does stress perfusion imaging improve the diagnostic accuracy of late gadolinium enhanced cardiac magnetic resonance for establishing the etiology of heart failure?
Background
Late gadolinium enhanced cardiovascular magnetic resonance (LGE-CMR) has excellent specificity, sensitivity and diagnostic accuracy for differentiating between ischemic cardiomyopathy (ICM) and non-ischemic dilated cardiomyopathy (NICM). CMR first-pass myocardial perfusion imaging (perfusion-CMR) may also play role in distinguishing heart failure of ischemic and non-ischemic origins, although the utility of additional of stress perfusion imaging in such patients is unclear. The aim of this retrospective study was to assess whether the addition of adenosine stress perfusion imaging to LGE-CMR is of incremental value for differentiating ICM and NICM in patients with severe left ventricular systolic dysfunction (LVSD) of uncertain etiology.
Methods
We retrospectively identified 100 consecutive adult patients (median age 69 years (IQR 59–73)) with severe LVSD (mean LV EF 26.6 ± 7.0%) referred for perfusion-CMR to establish the underlying etiology of heart failure. The cause of heart failure was first determined on examination of CMR cine and LGE images in isolation. Subsequent examination of complete adenosine stress perfusion-CMR studies (cine, LGE and perfusion images) was performed to identify whether this altered the initial diagnosis.
Results
On LGE-CMR, 38 patients were diagnosed with ICM, 46 with NICM and 16 with dual pathology. With perfusion-CMR, there were 39 ICM, 44 NICM and 17 dual pathology diagnoses. There was excellent agreement in diagnoses between LGE-CMR and perfusion-CMR (Îş 0.968, p<0.001). The addition of adenosine stress perfusion images to LGE-CMR altered the diagnosis in only two of the 100 patients.
Conclusion
The addition of adenosine stress perfusion-CMR to cine and LGE-CMR provides minimal incremental diagnostic yield for determining the etiology of heart failure in patients with severe LVSD
Discovery of an optical cocoon tail behind the runaway HD 185806
Studies on the circumstellar structures around evolved stars provide vital
information on the evolution of the parent star and the properties of the local
interstellar medium. In this work, we present the discovery and
characterization of an optical cocoon tail behind the star HD 185806. The
cocoon apex emission is puzzling, as it is detected in the infrared but shows
no signal in the optical wavelength. The H-alpha and [OIII] fluxes of the
nebular structure vary from 2.7 to 8.5x10^{-12} erg s^{-1} cm^ {-2} and from
0.9 to 7.0x10^{-13} erg s^{-1} cm^{-2}, respectively. Through high-resolution
spectroscopy, we derive the spectral type of the star, construct the
position-velocity diagrams of the cocoon tail for the H-alpha, [OIII] and [NII]
emission lines, and determine its velocity in the range of -100 to 40 km s
^{-1} . Furthermore, we use SED fitting and MESA evolutionary models adopting a
distance of 900 pc, and classify HD 185806 as a 1.3 M star, in the transition
phase between the RGB and early AGB stages. Finally, we study the
morpho-kinematic structure of the cocoon tail using the astronomical software
SHAPE. An ellipsoidal structure, with an inclination of 19 degrees with respect
to the plane of sky is found to better reproduce the observed cocoon tail of HD
185806.Comment: Accepted 2022 June 29. Received 2022 June 24; in original form 2022
May 26, 14 pages. Dedicated to V.G. who passed away on 2 Sept. 202
Diurnal and semidiurnal tidal currents in the deep mid-Arabian Sea
Current meter records from two depths, approximately 1000 and 3000 m, at three moorings in the deep mid-Arabian Sea were used to study tidal components. Tidal ellipses for the semi-diurnal (M2, S2 and K2) and the diurnal (K1, and P1) tidal constituents have been determined using the currents recorded at hourly intervals during May 1986-May 1987. The clockwise rotating M2 tidal currents were the strongest. The maximum horizontal velocities due to M2,S2 and K1 tides were 2.2 cm/s, l.0cm/s and 0.89 cm/s respectively. The amplitudes of the other two constituents (P1, and K2) were much smaller. The barotropic M2 ellipses have been estimated by averaging the M2 tidal currents at the upper and lower levels. Although the amplitudes of computed ellipses are lower than those that have been predicted using numerical models of global tidal model, their orientations are the same
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