4,664 research outputs found
Absolute dimensions of the G7+K7 eclipsing binary star IM Virginis: Discrepancies with stellar evolution models
We report extensive spectroscopic and differential photometric BVRI
observations of the active, detached, 1.309-day double-lined eclipsing binary
IM Vir, composed of a G7-type primary and a K7 secondary. With these
observations we derive accurate absolute masses and radii of M(1) = 0.981 +/-
0.012 M(Sun), M(2) = 0.6644 +/- 0.0048 M(Sun), R(1) = 1.061 +/- 0.016 R(Sun),
and R(2) = 0.681 +/- 0.013 R(Sun) for the primary and secondary, with relative
errors under 2%. The effective temperatures are 5570 +/- 100 K and 4250 +/- 130
K. The significant difference in mass makes this a favorable case for
comparison with stellar evolution theory. We find that both stars are larger
than the models predict, by 3.7% for the primary and 7.5% for the secondary, as
well as cooler than expected, by 100 K and 150 K, respectively. These
discrepancies are in line with previously reported differences in low-mass
stars, and are believed to be caused by chromospheric activity, which is not
accounted for in current models. The effect is not confined to low-mass stars:
the rapidly-rotating primary of IM Vir joins the growing list of objects of
near-solar mass (but still with convective envelopes) that show similar
anomalies. The comparison with the models suggests an age of 2.4 Gyr for the
system, and a metallicity [Fe/H] of approximately -0.3 that is consistent with
other indications, but requires confirmation.Comment: 14 pages, 13 figures. Accepted for publication in Ap
F-algebra–Rinehart pairs and super F-algebroids
We define F-algebra--Rinehart pairs and super F-algebroids and study theconnection between them.<br
The Mass-Radius(-Rotation?) Relation for Low-Mass Stars
The fundamental properties of low-mass stars are not as well understood as
those of their more massive counterparts. The best method for constraining
these properties, especially masses and radii, is to study eclipsing binary
systems, but only a small number of late-type (M0 or later) systems have been
identified and well-characterized to date. We present the discovery and
characterization of six new M dwarf eclipsing binary systems. The twelve stars
in these eclipsing systems have masses spanning 0.38-0.59 Msun and orbital
periods of 0.6--1.7 days, with typical uncertainties of ~0.3% in mass and
0.5--2.0% in radius. Combined with six known systems with high-precision
measurements, our results reveal an intriguing trend in the low-mass regime.
For stars with M=0.35-0.80 Msun, components in short-period binary systems (P<1
day; 12 stars) have radii which are inflated by up to 10% (mean=4.8+/-1.0%)
with respect to evolutionary models for low-mass main-sequence stars, whereas
components in longer-period systems (>1.5 days; 12 stars) tend to have smaller
radii (mean=1.7+/-0.7%). This trend supports the hypothesis that short-period
systems are inflated by the influence of the close companion, most likely
because they are tidally locked into very high rotation speeds that enhance
activity and inhibit convection. In summary, very close binary systems are not
representative of typical M dwarfs, but our results for longer-period systems
indicate that the evolutionary models are broadly valid in the M~0.35-0.80 Msun
regime.Comment: Accepted to ApJ; 21 pages, 10 figures, 8 tables in emulateapj format.
The full contents of Table 4 are included in the submission as tab4.tx
Green chemistry and environmental processes
Funding Information: Acknowledgments: Portuguese FCT—Fundação para a Ciência e a Tecnologia, I.P., under the Scientific Employment Stimulus—Institutional Call (CEECINST/00102/2018) and Associate Laboratory for Green Chemistry—LAQV, financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020) and the Spanish Project ref. RTI 2018-099224-B100 funded by ERDF/Ministry of Science, Innovation and Universities. S.M.-T. also acknowledges the Ramón y Cajal contract (RYC-2019-026634-I/AEI/10.13039/501100011033) from MINECO.publishersversionpublishe
Social policy in a global society : parallels and lessons from the Canada - Latin America experience
Meeting: Social Policy in a Global Society, 26-28 Oct. 1994, Ottawa, ON, C
Spitzer Infrared Observations and Independent Validation of the Transiting Super-Earth CoRoT-7b
The detection and characterization of the first transiting super-Earth,
CoRoT-7 b, has required an unprecedented effort in terms of telescope time and
analysis. Although the star does display a radial velocity signal at the period
of the planet, this has been difficult to disentangle from the intrinsic
stellar variability, and pinning down the velocity amplitude has been very
challenging. As a result, the precise value of the mass of the planet - and
even the extent to which it can be considered to be confirmed - have been
debated in the recent literature, with six mass measurements published so far
based on the same spectroscopic observations, ranging from about 2 to 8 Earth
masses. Here we report on an independent validation of the planet discovery,
using one of the fundamental properties of a transit signal: its achromaticity.
We observed four transits of CoRoT-7 b with Spitzer, in order to determine
whether the depth of the transit signal in the near-infrared is consistent with
that observed in the CoRoT bandpass, as expected for a planet. We detected the
transit and found an average depth of 0.426 {\pm} 0.115 mmag at 4.5 {\mu}m,
which is in good agreement with the depth of 0.350 {\pm} 0.011 mmag found by
CoRoT. These observations place important constraints on the kinds of
astrophysical false positives that could mimic the signal. Combining this with
additional constraints reported earlier, we performed an exhaustive exploration
of possible blends scenarios for CoRoT-7 b using the BLENDER technique. We are
able to rule out the vast majority of false positives, and the remaining ones
are found to be much less likely than a true transiting planet. We thus
validate CoRoT-7 b as a bona-fide planet with a very high degree of confidence,
independently of any radial-velocity information. Our Spitzer observations have
additionally allowed us to significantly improve the ephemeris of the planet.Comment: Accepted by Ap
LEARNING FOR THE GENERATION OF SHARED VALUE: CHALLENGE OF THE MANAGEMENT PROGRAM OF A PUBLIC UNIVERSITY
Companies as organizations focused on the fulfillment of particular objectives direct and maximizing limited resources in the function of satisfying needs in society, however, motivated by profit and rarely conceived of their investors as sufficient, causing neglect and distancing from the commitment to ethical and responsible management of resources, oriented by market orders, under policies more concerned with their profits than with operational practices that, in addition to improving their competitiveness, help to improve social conditions in a reactivation process after the pandemic experienced, contribute to the quality of life in general in the communities involved in their production processes, in other words, the generation of shared value (SV). The results of a study that sought to identify, through the perception delivered by students and graduates of an administration program of a public university, the level of perception of learning that allows contributing to the culture in the generation of shared value in organizations. It is a population that, due to its formation, challenges them with the transfer of knowledge that contributes to the economic reactivation, as well as to the generation of SV in the organizations. The study is based on Porter's and Kramer's ideas on preconceiving a) products and markets, b) redefining productivity in the value chain, and c) building support clusters. The methodology implemented for the analysis was mixed, using the survey as a data collection instrument. The results show that the students and graduates of the program observed show that there is a medium-low environment in the three concepts evaluated, with a medium level of 40%, a low level of 35% and a high level of only 24%
Learning For The Generation Of Shared Value: Challenge Of The Management Program Of A Public University
Companies as organizations focused on the fulfillment of particular objectives direct and maximizing limited resources in the function of satisfying needs in society, however, motivated by profit and rarely conceived of their investors as sufficient, causing neglect and distancing from the commitment to ethical and responsible management of resources, oriented by market orders, under policies more concerned with their profits than with operational practices that, in addition to improving their competitiveness, help to improve social conditions in a reactivation process after the pandemic experienced, contribute to the quality of life in general in the communities involved in their production processes, in other words, the generation of shared value (SV). The results of a study that sought to identify, through the perception delivered by students and graduates of an administration program of a public university, the level of perception of learning that allows contributing to the culture in the generation of shared value in organizations. It is a population that, due to its formation, challenges them with the transfer of knowledge that contributes to the economic reactivation, as well as to the generation of SV in the organizations. The study is based on Porter's and Kramer's ideas on preconceiving a) products and markets, b) redefining productivity in the value chain, and c) building support clusters. The methodology implemented for the analysis was mixed, using the survey as a data collection instrument. The results show that the students and graduates of the program observed show that there is a medium-low environment in the three concepts evaluated, with a medium level of 40%, a low level of 35% and a high level of only 24%
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