Low mass binary neutron star mergers : gravitational waves and neutrino emission - INSPIRE-HEP
Our measurements are consistent with the mass–radius relation and we determine and radius of the low-mass companion star, Msec = ± . epoch SDSS photometric survey, known as Stripe 82 (Becker et al. the stellar mass-luminosity relationship (Figure ), or the Main Sequence of hydrogen burning stars in the luminosity-temperature diagram (Fig- ure ). According to these results, on the mass-radius plane, the regions The mass- radius relation for these stars is determined in the third part of .. individual stripes labeled in the figure as CSD for carbon, MgSD for magnesium and FeSD for iron.
In this section, we study the possibility that starspots could be responsible for systematic effects inherent to the light curve and radial velocity analyses in the case of the very active low-mass eclipsing binaries. We analyze whether the fundamental properties determined from the classical modeling could be biased because of the presence of starspots in different geometries.
 The mass-radius relationship from solar-type stars to terrestrial planets: a review
Radial velocity curves provide values for the mass ratio q and projected semimajor axis asin i. The combination of the two modeling procedures yields the absolute properties of the components independent of models or distance calibrations.
Radiative parameters, such as limb darkening and gravity darkening, relevant for light curve analyses, are usually taken from theory. The presence of spots on the surface of the components of an EB system causes perturbations on both the light and radial velocity curves. The most prominent effect is on light curves, in which modulations in the out-of-eclipse phases appear due to the transit and occultation of spots according to the orbital and spin motions. To appropriately derive physical properties of the components, the spot effect must be taken into account when analyzing these curves.
The WD code introduces spots on the modeling assuming that they are circular and that they have a uniform temperature ratio with respect to the photosphere.
This model can reproduce the presence of complex and irregular spot groups by equivalent circular spots with an average temperature. The total luminosity of a spotted star is the addition of the contribution of the spots at an effective temperature Teff,s and the immaculate surface at Teff.
Hot spots can be interpreted as photospheric regions surrounded by large cool spots. This value is much smaller than the range between 0. It must be mentioned, though, that since the relevant measures in EB light curve analyses are differential magnitudes, the photometric variations used to derive the spot parameters are not sensitive to the total surface covered by spots but to the contrast between areas with different effective temperatures.
For instance, an evenly spotted star would not show significant light curve variations. Such theoretical light curves were subsequently compared with those observed in EBs. We have developed a code to randomly place spots on the surface of stars. We assumed a uniform longitude distribution and tried different distributions over latitude.
- THE EFFECT OF MAGNETIC ACTIVITY ON LOW-MASS STARS IN ECLIPSING BINARIES
- mass-radius relation
Thus, we decided to extend the distribution to all stellar latitudes. This roughly mimics distributions of 0.
For comparison, we also considered a bilinear distribution from the pole to 70 deg with a peak at 25 deg. This is similar to the 0. Finally, we considered a completely uniform distribution. Additionally, to have reasonable computing time using the WD code, we limited the number of spots by imposing that the centers of two spots could not be closer than half their radius, i. Stars with too little mass do not have enough gravitational compression in their cores to produce the required high temperatures and densities needed for fusion of ordinary hydrogen.
The lowest mass is about 0. A star less massive than this does not undergo fusion of ordinary hydrogen but if it is more massive than about 13 Jupiters it can fuse the heavier isotope of hydrogen, deuterium, in the first part of its life.
Stars in this boundary zone between ordinary stars and gas planets are called brown dwarfs. After whatever deuterium fusion it does while it is young, a brown dwarf then just slowly radiates away the heat from that fusion and that is left over from its formation.
Among the first brown dwarfs discovered is the companion orbiting the star Gliese Selecting the picture below of Gliese and its companion, Gliese B, will take you to the caption for the picture at the Space Telescope Institute. With the discovery of several hundred brown dwarfs in recent infrared surveys, astronomers have now extended the spectral type sequence to include these non-planets.
Just beyond the M-stars are the L dwarfs with surface temperatures of about K to K with strong absorption lines of metal hydrides and alkali metals. Cooler than the L dwarfs are the T dwarfs. At their cooler temperatures, methane lines become prominent. Stars with too much mass have so much radiation pressure inside pushing outward on the upper layers, that the star is unstable.
It blows off the excess mass. The limit is roughly about to perhaps solar masses. The picture of Eta Carinae below shows two dumbbell-shaped lobes of ejected material from the star in an earlier episode of mass ejection. Selecting the image will take you to more information about the image at the Space Telescope Institute will display in another window. The picture below from the Hubble Space Telescope shows the violet Pistol Star surrounded by hydrogen gas fluorescing from the copious ultraviolet light coming from the star.
Selecting the image will bring up the press release from the Space Telescope Institute in another window.