The structure and evolution of quasi-stars Ball, Warrick H.; Tout, Christopher A.; Żytkow, Anna N. ...
Monthly Notices of the Royal Astronomical Society,
July 2011, Letnik:
414, Številka:
3
Journal Article
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The existence of bright quasars at high redshifts implies that supermassive black holes were able to form in the early Universe. Though a number of mechanisms to achieve this have been proposed, none ...yet stands out. A recent suggestion is the formation of quasi-stars, initially stellar-mass black holes accreting from hydrostatic giant-like envelopes of gas, formed from the monolithic collapse of pre-galactic gas clouds. In this work, we modify the Cambridge stars stellar evolution package to construct detailed models of the evolution of these objects. We find that, in all of our models, the black hole inside the envelope is able to reach slightly more than one-tenth of the total mass of the system before hydrostatic equilibrium breaks down. This breakdown occurs after a few million years of evolution. We show that the mechanism which causes the hydrostatic evolution to end is present in polytropic models. We also show that the solutions are highly sensitive to the size of the inner boundary radius and that no physical solutions exist if the inner boundary is chosen to be less than about 0.3 of the Bondi radius.
In this erratum, we provide corrected sets of r 01,10,02 difference ratio values and associated uncertainties, which were overestimated in the original paper (as noted by Roxburgh 2017) due to a ...missing trimming in the post-processing of the Markov chain Monte Carlo (MCMC) chains for these values. The typical reduction in the ratio uncertainties from performing the trimming is a factor of 10 (see Figure 3). Other parameters optimized in the peak-bagging (for instance, individual mode frequencies) are unaffected, as the trimming was performed for these in the original work (Lund et al. 2017). We also provide updated values for the n D 2 values of l=3 modes. We note that the values presented here, as with those presented in the original work, are obtained from a single peak-bagging procedure (see Lund et al. 2017 for details) and have yet to be verified by independent analyses using the same input power spectra. Examples of the updated tables from the original paper are given in Tables 1-3. We note that tables with individual mode parameters (Table 2) have been added for completeness, but the parameters in these tables are unchanged compared to the original paper. In addition to the corrected values mentioned above, we provide covariance matrices for the mode frequencies, frequency difference ratios (r 01,10,02), and second differences (n D 2) for the LEGACY sample (Lund et al. 2017), which were not published with the original work. The values provided by this erratum will be available in the online version of the paper. Figure 1. Comparison between ratio distribution of = r n 01, 25 (n » m 3090 Hz) for KIC 9139151 from the full (green) and properly thinned MCMC chains (black). The dashed red line (on top of the black curve) shows the distribution obtained by sampling from the reported frequency values and corresponding uncertainties (assuming that these are normally distributed and uncorrelated). The central peak is captured by both distributions, but the wide background signal representing the ratio prior has disappeared from the thinned chains. Dotted lines indicate the distribution medians; dashed lines bound the corresponding 68% highest probability density intervals.
Asteroseismic methods offer a means to investigate stellar activity and activity cycles as well as to identify those properties of stars which are crucial for the operation of stellar dynamos. With ...data from CoRoT and Kepler, signatures of magnetic activity have been found in the seismic properties of a few dozen stars. Now, NASA's Transiting Exoplanet Survey Satellite (TESS) mission offers the possibility to expand this, so far, rather exclusive group of stars. This promises to deliver new insight into the parameters that govern stellar magnetic activity as a function of stellar mass, age, and rotation rate. We derive a new scaling relation for the amplitude of the activity-related acoustic (p-mode) frequency shifts that can be expected over a full stellar cycle. Building on a catalog of synthetic TESS time series, we use the shifts obtained from this relation and simulate the yield of detectable frequency shifts in an extended TESS mission. We find that, according to our scaling relation, we can expect to find significant p-mode frequency shifts for a couple hundred main-sequence and early subgiant stars and for a few thousand late subgiant and low-luminosity red giant stars.
The TESS light curve of AI Phoenicis Maxted, P F L; Gaulme, Patrick; Graczyk, D ...
Monthly Notices of the Royal Astronomical Society,
10/2020, Letnik:
498, Številka:
1
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ABSTRACT
Accurate masses and radii for normal stars derived from observations of detached eclipsing binary stars are of fundamental importance for testing stellar models and may be useful for ...calibrating free parameters in these model if the masses and radii are sufficiently precise and accurate. We aim to measure precise masses and radii for the stars in the bright eclipsing binary AI Phe, and to quantify the level of systematic error in these estimates. We use several different methods to model the Transiting Exoplanet Survey Satellite (TESS) light curve of AI Phe combined with spectroscopic orbits from multiple sources to estimate precisely the stellar masses and radii together with robust error estimates. We find that the agreement between different methods for the light-curve analysis is very good but some methods underestimate the errors on the model parameters. The semi-amplitudes of the spectroscopic orbits derived from spectra obtained with modern échelle spectrographs are consistent to within 0.1 per cent. The masses of the stars in AI Phe are $M_1 = 1.1938 \pm 0.0008\, \rm M_{\odot }$ and $M_2 = 1.2438 \pm 0.0008\, \rm M_{\odot }$, and the radii are $R_1 = 1.8050 \pm 0.0022\, \rm R_{\odot }$ and $R_2 = 2.9332 \pm 0.0023\, \rm R_{\odot }$. We conclude that it is possible to measure accurate masses and radii for stars in bright eclipsing binary stars to a precision of 0.2 per cent or better using photometry from TESS and spectroscopy obtained with modern échelle spectrographs. We provide recommendations for publishing masses and radii of eclipsing binary stars at this level of precision.
Robust age estimates of red giant stars are now possible thanks to the precise inference of their mass based on asteroseismic constraints. However, there are cases where such age estimates can be ...highly precise yet very inaccurate. An example is giants that have undergone mass loss or mass transfer events that have significantly altered their mass. In this context, stars with ‘apparent’ ages significantly higher than the age of the Universe are candidates for stripped stars, or stars that have lost more mass than expected, most likely via interactions with a companion star or because of the poorly understood mass-loss mechanism along the red-giant branch. In this work we identify examples of such objects among red giants observed by
Kepler
, both at low (Fe/H ≲ −0.5) and solar metallicity. By modelling their structure and pulsation spectra, we find a consistent picture that confirms that they are indeed low-mass objects consisting of a He core of ≈0.5
M
⊙
and an envelope of ≈0.1 − 0.2
M
⊙
. Moreover, we find that these stars are characterised by a rather extreme coupling (
q
≳ 0.4) between the pressure-mode and gravity-mode cavities, one that is much higher than the typical value for red clump stars, thus providing a direct seismic signature of their peculiar structure. The complex pulsation spectra of these objects, if observed with sufficient frequency resolution, hold detailed information about the structural properties of likely products of mass stripping and can hence potentially shed light on their formation mechanism. On the other hand, our tests highlight the difficulties associated with reliably measuring the large frequency separation, especially in shorter datasets, which impacts the reliability of the inferred masses and ages of low-mass red clump stars with, for example, K2 or TESS data.
Context.
The Transiting Exoplanet Survey Satellite (TESS) mission has provided photometric light curves for stars across nearly the entire sky. This allows for the application of asteroseismology to ...a pool of potential solar-like oscillators that is unprecedented in size.
Aims.
We aim to produce a catalogue of solar-like oscillators observed by TESS in the 120-s and 20-s cadence modes. The catalogue is intended to highlight stars oscillating at frequencies above the TESS 30-min cadence Nyquist frequency with the purpose of encompassing the main-sequence and subgiant evolutionary phases. We aim to provide estimates for the global asteroseismic parameters
v
max
and ∆
v
.
Methods.
We applied a new probabilistic detection algorithm to the 120-s and 20-s light curves of over 250 000 stars. This algorithm flags targets that show characteristic signatures of solar-like oscillations. We manually vetted the resulting list of targets to confirm the presence of solar-like oscillations. Using the probability densities computed by the algorithm, we measured the global asteroseismic parameters
v
max
and ∆
v
.
Results.
We produce a catalogue of 4177 solar-like oscillators, reporting ∆
v
and
v
max
for 98% of the total star count. The asteroseismic data reveal a vast coverage of the Hertzsprung-Russell diagram, populating the red giant branch, the subgiant regime, and extending towards the main sequence.
Conclusions.
A crossmatch with external catalogues shows that 25 of the detected solar-like oscillators are a component of a spectroscopic binary, and 28 are confirmed planet host stars. These results provide the potential for precise, independent asteroseismic constraints on these and any additional TESS targets of interest.
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