scholarly journals Can Self-Replicating Species Flourish in the Interior of a Star?

2020 ◽  
Author(s):  
Luis Anchordoqui ◽  
Eugene M. Chudnovsky
Keyword(s):  
Low Temperature ◽  
Nucleic Acids ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Atoms And Molecules ◽  
Form Of Life ◽  
Advanced Form ◽  
Life On Earth

The existing view of biological life is that it evolves under suitable conditions in the low-temperature world of atoms and molecules on the surface of a planet. It is believed that any plausible extraterrestrial form of life must resemble the life on Earth that is ruled by biochemistry of nucleic acids, proteins, and sugars. Going against this dogma, we argue that an advanced form of life based upon short-lived species can exist inside main-sequence stars like our Sun.

scholarly journals Lithium abundances in late main sequence stars. The case of the hyades

1984 ◽  
Vol 105 ◽  
pp. 529-531
Author(s):  
A. Baglin ◽  
P.J. Morel
Keyword(s):  
Low Temperature ◽  
Transport Process ◽  
Main Sequence ◽  
Light Elements ◽  
Main Sequence Stars

It is well known that light elements like lithium are good indicators of the hydrodynamical behaviour of the outerlayers of the stars. As they are nuclearly destroyed at low temperature, i.e. close to the surface, their surface abundances reflect the nature of the transport process at work between the photosphere and the nuclear destruction region.

scholarly journals Which stars can see Earth as a transiting exoplanet?

2020 ◽  
Vol 499 (1) ◽  
pp. L111-L115
Author(s):  
L Kaltenegger ◽  
J Pepper
Keyword(s):  
Main Sequence ◽  
Line Of Sight ◽  
Main Sequence Stars ◽  
Target List ◽  
Distant Observer ◽  
Spectroscopic Observations ◽  
Transiting Planets ◽  
Vantage Points ◽  
Life On Earth ◽  
Gaia Dr2

ABSTRACT Transit observations have found the majority of exoplanets to date. Also spectroscopic observations of transits and eclipses are the most commonly used tool to characterize exoplanet atmospheres and will be used in the search for life. However, an exoplanet’s orbit must be aligned with our line of sight to observe a transit. Here, we ask, from which stellar vantage points would a distant observer be able to search for life on Earth in the same way? We use the TESS Input Catalog and data from Gaia DR2 to identify the closest stars that could see Earth as a transiting exoplanet: We identify 1004 main-sequence stars within 100 parsecs, of which 508 guarantee a minimum 10-h long observation of Earth’s transit. Our star list consists of about 77 percent M-type, 12 percent K-type, 6 percent G-type, 4 percent F-type stars, and 1 percent A-type stars close to the ecliptic. SETI searches like the Breakthrough Listen Initiative are already focusing on this part of the sky. Our catalogue now provides a target list for this search. As part of the extended mission, NASA’s TESS will also search for transiting planets in the ecliptic to find planets that could already have found life on our transiting Earth .

scholarly journals Astrobiological effects of F, G, K and M main-sequence stars

2007 ◽  
Vol 3 (S249) ◽  
pp. 203-206 ◽  
Author(s):  
M. Cuntz ◽  
L. Gurdemir ◽  
E. F. Guinan ◽  
R. L. Kurucz
Keyword(s):  
Main Sequence ◽  
Life Forms ◽  
Main Sequence Stars ◽  
Extraterrestrial Life ◽  
Atoms And Molecules ◽  
Habitable Zones ◽  
Carbon Based

AbstractWe focus on the astrobiological effects of photospheric radiation produced by main-sequence stars of spectral types F, G, K, and M. The photospheric radiation is represented by using realistic spectra, taking into account millions or hundred of millions of lines for atoms and molecules. DNA is taken as a proxy for carbon-based macromolecules, assumed to be the chemical centerpiece of extraterrestrial life forms. Emphasis is placed on the investigation of the radiative environment in conservative as well as generalized habitable zones.

scholarly journals Calibration of The Main Sequence Stars: Alpha Centauri

1993 ◽  
Vol 137 ◽  
pp. 383-385
Author(s):  
C. Neuforge
Keyword(s):  
Low Temperature ◽  
Main Sequence ◽  
Main Sequence Stars

AbstractNew low temperature opacities have been computed and applied together with the new OPAL opacities to recalibrate the α Centauri system. Our solution is in favour of a Z value of about twice Z⊙.

Chromospheric activity as a function of age in main-sequence stars

1966 ◽  
Vol 24 ◽  
pp. 40-43
Author(s):  
O. C. Wilson ◽  
A. Skumanich
Keyword(s):  
Main Sequence ◽  
The Sun ◽  
Main Sequence Stars ◽  
Tentative Conclusion ◽  
Chromospheric Activity ◽  
General Field ◽  
Large Clusters

Evidence previously presented by one of the authors (1) suggests strongly that chromospheric activity decreases with age in main sequence stars. This tentative conclusion rests principally upon a comparison of the members of large clusters (Hyades, Praesepe, Pleiades) with non-cluster objects in the general field, including the Sun. It is at least conceivable, however, that cluster and non-cluster stars might differ in some fundamental fashion which could influence the degree of chromospheric activity, and that the observed differences in chromospheric activity would then be attributable to the circumstances of stellar origin rather than to age.

On The Radii of Ap Stars

1976 ◽  
Vol 32 ◽  
pp. 49-55 ◽  
Author(s):  
F.A. Catalano ◽  
G. Strazzulla
Keyword(s):  
Observational Data ◽  
Line Width ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Ap Stars

SummaryFrom the analysis of the observational data of about 100 Ap stars, the radii have been computed under the assumption that Ap are main sequence stars. Radii range from 1.4 to 4.9 solar units. These values are all compatible with the Deutsch's period versus line-width relation.

Pre–Main-Sequence Stars in the Young Galactic Cluster IC 4996: A CCD Photometric Study

1998 ◽  
Vol 116 (4) ◽  
pp. 1801-1809 ◽  
Author(s):  
Antonio J. Delgado ◽  
Emilio J. Alfaro ◽  
André Moitinho ◽  
José Franco
Keyword(s):  
Main Sequence ◽  
Photometric Study ◽  
Main Sequence Stars ◽  
Galactic Cluster

Photoionized and Photodissociated Regions around Main‐Sequence Stars

1998 ◽  
Vol 501 (1) ◽  
pp. 192-206 ◽  
Author(s):  
Rosa Izela Diaz‐Miller ◽  
Jose Franco ◽  
Steven N. Shore
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars

scholarly journals Helium, [Fe/H] Abundances and the HR (Log TEFF, MBol) Diagram With Hipparcos Data of The Four Nearest Open Clusters: Hyades, Coma Berenices, The Pleiades and Praesepe

1998 ◽  
Vol 11 (1) ◽  
pp. 565-565
Author(s):  
G. Cayrel de Strobel ◽  
R. Cayrel ◽  
Y. Lebreton
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Main Sequence Stars ◽  
Spectroscopic Analyses ◽  
Solar Metallicity ◽  
Metal Abundances ◽  
The Mean ◽  
The Moment ◽  
The One ◽  
Best Fit

After having studied in great detail the observational HR diagram (log Teff, Mbol) composed by 40 main sequence stars of the Hyades (Perryman et al.,1997, A&A., in press), we have tried to apply the same method to the observational main sequences of the three next nearest open clusters: Coma Berenices, the Pleiades, and Praesepe. This method consists in comparing the observational main sequence of the clusters with a grid of theoretical ZAMSs. The stars composing the observational main sequences had to have reliable absolute bolometric magnitudes, coming all from individual Hipparcos parallaxes, precise bolometric corrections, effective temperatures and metal abundances from high resolution detailed spectroscopic analyses. If we assume, following the work by Fernandez et al. (1996, A&A,311,127), that the mixing-lenth parameter is solar, the position of a theoretical ZAMS, in the (log Teff, Mbol) plane, computed with given input physics, only depends on two free parameters: the He content Y by mass, and the metallicity Z by mass. If effective temperature and metallicity of the constituting stars of the 4 clusters are previously known by means of detailed analyses, one can deduce their helium abundances by means of an appropriate grid of theoretical ZAMS’s. The comparison between the empirical (log Teff, Mbol) main sequence of the Hyades and the computed ZAMS corresponding to the observed metallicity Z of the Hyades (Z= 0.0240 ± 0.0085) gives a He abundance for the Hyades, Y= 0.26 ± 0.02. Our interpretation, concerning the observational position of the main sequence of the three nearest clusters after the Hyades, is still under way and appears to be greatly more difficult than for the Hyades. For the moment we can say that: ‒ The 15 dwarfs analysed in detailed in Coma have a solar metallicity: [Fe/H] = -0.05 ± 0.06. However, their observational main sequence fit better with the Hyades ZAMS. ‒ The mean metallicity of 13 Pleiades dwarfs analysed in detail is solar. A metal deficient and He normal ZAMS would fit better. But, a warning for absorption in the Pleiades has to be recalled. ‒ The upper main sequence of Praesepe, (the more distant cluster: 180 pc) composed by 11 stars, analysed in detail, is the one which has the best fit with the Hyades ZAMS. The deduced ‘turnoff age’ of the cluster is slightly higher than that of the Hyades: 0.8 Gyr instead of 0.63 Gyr.

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