Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe masses, radii and luminosities of the components of U Geminorum
45
0
0.0
(
0
)
Authors
T. Naylor University of Exeter
Ask ChatGPT about the research
No Arabic abstract
We present a phase-resolved spectroscopic study of the secondary star in the cataclysmic variable U Gem. We use our data to measure the radial velocity semi-amplitude, systemic velocity and rotational velocity of the secondary star. Combining this with literature data allows us to determine masses and radii for both the secondary star and white dwarf which are independent of any assumptions about their structure. We use these to compare their properties with those of field stars and find that both components follow field mass-radius relationships. The secondary star has the mass, radius, luminosity and photometric temperature of an M2 star, but a spectroscopic temperature of M4. The latter may well be due to a high metallicity. There is a troubling inconsistency between the radius of the white dwarf inferred from its gravitational redshift and inclination and that inferred from its temperature, flux, and astrometric distance. We find that there are two fundamental limits to the accuracy of the parameters we can derive. First the radial velocity curve of the secondary star deviates from a sinusoid, in part because of its asphericity (which can be modelled) and in part because the line flux is not evenly distributed over its surface. Second we cannot be certain which spectral type is the best match for the lines of the secondary star, and the derived rotational velocity is a function of the spectral type of the template star used.
rate research
Read More
We discuss new limits on masses and radii of compact stars and we conclude that they can be interpreted as an indication of the existence of two classes of stars: normal compact stars and ultra-compact stars. We estimate the critical mass at which the first configuration collapses into the second.
Double-lined spectroscopic binaries (SB2s) are one of the main sources of stellar masses, as additional observations are only needed to give the inclinations of the orbital planes in order to obtain the individual masses of the components. For this reason, we are observing a selection of SB2s using the SOPHIE spectrograph at the Haute-Provence observatory in order to precisely determine their orbital elements. Our objective is to finally obtain masses with an accuracy of the order of one percent by combining our radial velocity (RV) measurements and the astrometric measurements that will come from the Gaia satellite. We present here the RVs and the re-determined orbits of 10 SB2s. In order to verify the masses we will derive from Gaia, we obtained interferometric measurements of the ESO VLTI for one of these SB2s. Adding the interferometric or speckle measurements already published by us or by others for 4 other stars, we finally obtain the masses of the components of 5 binary stars, with masses ranging from 0.51 to 2.2 solar masses, including main-sequence dwarfs and some more evolved stars whose location in the HR diagram has been estimated.
We present an analysis of the 4-2600 $mu$m spectral energy distributions (SEDs) of the west and east nuclei and the diffuse infrared (IR) region of the merger-driven starburst Arp 220. We examine several possible source morphologies and dust temperature distributions using a mixture of silicate and carbonaceous grains. From fits to the SEDs we derive dust masses, temperatures, luminosities, and dust inferred gas masses. We show that the west and east nuclei are powered by central sources deeply enshrouded behind $sim 10^{26}$ cm$^{-2}$ column densities of hydrogen with an exponential density distribution, and that the west and east nuclei are optically thick out to wavelengths of $sim 1900$ and $sim 770$ $mu$m, respectively. The nature of the central sources cannot be determined from our analysis. We derive star formation rates or black hole masses needed to power the IR emission, and show that the [C II] 158$mu$m line cannot be used as a tracer of the star formation rate in heavily obscured systems. Dust inferred gas masses are larger than those inferred from CO observations, suggesting either larger dust-to-H mass ratios, or the presence of hidden atomic H that cannot be inferred from CO observations. The luminosities per unit mass in the nuclei are $sim 450$, in solar units, smaller that the Eddington limit of $sim 1000 - 3000$ for an optically thick star forming region, suggesting that the observed gas outflows are primarily driven by stellar winds and supernova shock waves instead of radiation pressure on the dust.
High-resolution spectroscopy of U Gem was obtained during quiescence. We did not find a hot spot or gas stream around the outer boundaries of the accretion disk. Instead, we detected a strong narrow emission near the location of the secondary star. We measured the radial velocity curve from the wings of the double-peaked H$alpha$ emission line, and obtained a semi-amplitude value that is in excellent agreement with the obtained from observations in the ultraviolet spectral region by Sion et al. (1998). We present also a new method to obtain K_2, which enhances the detection of absorption or emission features arising in the late-type companion. Our results are compared with published values derived from the near-infrared NaI line doublet. From a comparison of the TiO band with those of late type M stars, we find that a best fit is obtained for a M6V star, contributing 5 percent of the total light at that spectral region. Assuming that the radial velocity semi-amplitudes reflect accurately the motion of the binary components, then from our results: K_em = 107+/-2 km/s; K_abs = 310+/-5 km/s, and using the inclination angle given by Zhang & Robinson(1987); i = 69.7+/-0.7, the system parameters become: M_WD = 1.20+/-0.05 M_sun,; M_RD = 0.42+/-0.04 M_sun; and a = 1.55+/- 0.02 R_sun. Based on the separation of the double emission peaks, we calculate an outer disk radius of R_out/a ~0.61, close to the distance of the inner Lagrangian point L_1/a~0.63. Therefore we suggest that, at the time of observations, the accretion disk was filling the Roche-Lobe of the primary, and that the matter leaving the L_1 point was colliding with the disc directly, producing the hot spot at this location.
We combine equation of state of dense matter up to twice nuclear saturation density ($n_{rm sat}=0.16, text{fm}^{-3}$) obtained using chiral effective field theory ($chi$EFT), and recent observations of neutron stars to gain insights about the high-density matter encountered in their cores. A key element in our study is the recent Bayesian analysis of correlated EFT truncation errors based on order-by-order calculations up to next-to-next-to-next-to-leading order in the $chi$EFT expansion. We refine the bounds on the maximum mass imposed by causality at high densities, and provide stringent limits on the maximum and minimum radii of $sim1.4,{rm M}_{odot}$ and $sim2.0,{rm M}_{odot}$ stars. Including $chi$EFT predictions from $n_{rm sat}$ to $2,n_{rm sat}$ reduces the permitted ranges of the radius of a $1.4,{rm M}_{odot}$ star, $R_{1.4}$, by $sim3.5, text{km}$. If observations indicate $R_{1.4}<11.2, text{km}$, our study implies that either the squared speed of sound $c^2_{s}>1/2$ for densities above $2,n_{rm sat}$, or that $chi$EFT breaks down below $2,n_{rm sat}$. We also comment on the nature of the secondary compact object in GW190814 with mass $simeq 2.6,{rm M}_{odot}$, and discuss the implications of massive neutron stars $>2.1 ,{rm M}_{odot},(2.6,{rm M}_{odot})$ in future radio and gravitational-wave searches. Some form of strongly interacting matter with $c^2_{s}>0.35, (0.55)$ must be realized in the cores of such massive neutron stars. In the absence of phase transitions below $2,n_{rm sat}$, the small tidal deformability inferred from GW170817 lends support for the relatively small pressure predicted by $chi$EFT for the baryon density $n_{rm B}$ in the range $1-2,n_{rm sat}$. Together they imply that the rapid stiffening required to support a high maximum mass should occur only when $n_{rm B} gtrsim 1.5-1.8,n_{rm sat}$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
