14 research outputs found
AU Pegasi revisited: period evolution and orbital elements of a peculiar Type II Cepheid
New analysis on the period changes of Type II Cepheid AU Peg is presented.
The available recent photometric measurements were collected and analysed with
various methods. The period has been found to be constant for certain time
intervals, although increasing in overall, in contrast with the previous
expectations, which suggested the period change to reverse. Superimposed on
overall period change, a formerly unknown periodic behaviour has been found in
the diagram of AU Peg, which cannot be matched to the radial velocity
variations. Since the Cepheid is a member of a binary system, it is probable
that the unusual period change is in connection with the companion's tidal
force. The orbital elements of the binary system involving AU Peg have been
also revised.Comment: 8 pages, 8 figures, accepted for publication in Astrophysics and
Space Scienc
The effect of emission lines on the performance of photometric redshift estimation algorithms
We investigate the effect of strong emission line galaxies on the performance
of empirical photometric redshift estimation methods. In order to artificially
control the contribution of photometric error and emission lines to total flux,
we develop a PCA-based stochastic mock catalogue generation technique that
allows for generating infinite signal-to-noise ratio model spectra with
realistic emission lines on top of theoretical stellar continua. Instead of
running the computationally expensive stellar population synthesis and nebular
emission codes, our algorithm generates realistic spectra with a statistical
approach, and - as an alternative to attempting to constrain the priors on
input model parameters - works by matching output observational parameters.
Hence, it can be used to match the luminosity, colour, emission line and
photometric error distribution of any photometric sample with sufficient
flux-calibrated spectroscopic follow-up. We test three simple empirical
photometric estimation methods and compare the results with and without
photometric noise and strong emission lines. While photometric noise clearly
dominates the uncertainty of photometric redshift estimates, the key findings
are that emission lines play a significant role in resolving colour space
degeneracies and good spectroscopic coverage of the entire colour space is
necessary to achieve good results with empirical photo-z methods. Template
fitting methods, on the other hand, must use a template set with sufficient
variation in emission line strengths and ratios, or even better, first estimate
the redshift empirically and fit the colours with templates at the best-fit
redshift to calculate the K-correction and various physical parameters.Comment: 18 pages, 19 figures, Accepted for publication in MNRA
AU Pegasi revisited: period evolution and orbital elements of a peculiar Type II Cepheid
New analysis on the period changes of Type II Cepheid AU Peg is presented. The available recent photometric measurements were collecte and analysed with various methods. The period has been found to b constant for certain time intervals, although increasing in overall, i contrast with the previous expectations, which suggested the perio change to reverse. Superimposed on overall period change, a formerl unknown periodic behaviour has been found in the O-C diagram of AU Peg which cannot be matched to the radial velocity variations. Since th Cepheid is a member of a binary system, it is probable that the unusua period change is in connection with the companion's tidal force. Th orbital elements of the binary system involving AU Peg have been als revised
Family dispute: do Type IIP supernova siblings agree on their distance?
Context: Type II supernovae provide a direct way to estimate distances
through the expanding photosphere method, which is independent of the cosmic
distance ladder. A recently introduced Gaussian process-based method allows for
a fast and precise modelling of spectral time series, which puts accurate and
computationally cheap Type II-based absolute distance determinations within
reach.
Aims: The goal of the paper is to assess the internal consistency of this new
modelling technique coupled with the distance estimation empirically, using the
spectral time series of supernova siblings, i.e. supernovae that exploded in
the same host galaxy.
Methods: We use a recently developed spectral emulator code, which is trained
on \textsc{Tardis} radiative transfer models and is capable of a fast maximum
likelihood parameter estimation and spectral fitting. After calculating the
relevant physical parameters of supernovae we apply the expanding photosphere
method to estimate their distances. Finally, we test the consistency of the
obtained values by applying the formalism of Bayes factors.
Results: The distances to four different host galaxies were estimated based
on two supernovae in each. The distance estimates are not only consistent
within the errors for each of the supernova sibling pairs, but in the case of
two hosts they are precise to better than 5\%.
Conclusions: Even though the literature data we used was not tailored for the
requirements of our analysis, the agreement of the final estimates shows that
the method is robust and is capable of inferring both precise and consistent
distances. By using high-quality spectral time series, this method can provide
precise distance estimates independent of the distance ladder, which are of
high value for cosmology.Comment: 20 pages, 20 figures, 6 tables, Accepted in A&
A Multi-epoch, Multiwavelength Study of the Classical FUor V1515 Cyg Approaching Quiescence
Historically, FU Orionis-type stars are low-mass, pre-main-sequence stars. The members of this class experience powerful accretion outbursts and remain in an enhanced accretion state for decades or centuries. V1515 Cyg, a classical FUor, started brightening in the 1940s and reached its peak brightness in the late 1970s. Following a sudden decrease in brightness, it stayed in a minimum state for a few months, then started brightening for several years. We present the results of our ground-based photometric monitoring complemented with optical/near-infrared spectroscopic monitoring. Our light curves show a long-term fading with strong variability on weekly and monthly timescales. The optical spectra show P Cygni profiles and broad blueshifted absorption lines, common properties of FUors. However, V1515 Cyg lacks the P Cygni profile in the Ca II 8498 Å line, a part of the Ca infrared triplet, formed by an outflowing wind, suggesting that the absorbing gas in the wind is optically thin. The newly obtained near-infrared spectrum shows the strengthening of the CO bandhead and the FeH molecular band, indicating that the disk has become cooler since the last spectroscopic observation in 2015. The current luminosity of the accretion disk dropped from the peak value of 138 L ⊙ to about 45 L ⊙, suggesting that the long-term fading is also partly caused by the dropping of the accretion rate
Mid-infrared time-domain study of recent dust production events in the extreme debris disc of TYC 4209-1322-1
Extreme debris discs are characterized by unusually strong mid-infrared excess emission, which often proves to be variable. The warm dust in these discs is of transient nature and is likely related to a recent giant collision occurring close to the star in the terrestrial region. Here we present the results of a 877 days long, gap-free photometric monitoring performed by the Spitzer Space Telescope of the recently discovered extreme debris disc around TYC 4209-1322-1. By combining these observations with other time-domain optical and mid-infrared data, we explore the disc variability of the last four decades, with particular emphasis on the last 12 years. During the latter interval the disc showed substantial changes, the most significant was the brightening and subsequent fading between 2014 and 2018 as outlined in WISE data. The Spitzer light curves outline the fading phase and a subsequent new brightening of the disc after 2018, revealing an additional flux modulation with a period of ~39 days on top of the long-term trend. We found that all these variations can be interpreted as the outcome of a giant collision that happened at an orbital radius of ~0.3 au sometime in 2014. Our analysis implies that a collision on a similar scale could have taken place around 2010, too. The fact that the disc was already peculiarly dust rich 40 years ago, as implied by IRAS data, suggests that these dust production events belong to a chain of large impacts triggered by an earlier even more catastrophic collision
Improved emission line based classification of galaxies
Munkám során egy olyan új, emissziós vonalakon alapuló galaxisklasszifikációs módszert valósítottam meg, amely a meglévő gépi tanuláson alapuló algoritmusokhoz hasonló pontossággal rendelkezik, azonban azokkal ellentétben robusztusabb az emissziós vonalak észlelt tartományból vöröseltolódás miatt fellépő kitolódásával szemben. A módszer továbbá lehetővé teszi a vöröseltolódás miatt nem észlelhető vonalak erősségének becslését is, mely a jövőbeni galaxisevolúciós tanulmányok egyik fő eleme lehet
Independent study and spectral classification of a sample of poorly studied high proper motion M-dwarf candidate stars
We report an independent spectral classification of a sample of poorly studied M-dwarf candidate stars observed with the OSIRIS instrument a GTC. Our project was carried out as an independent test of the spectra classification. It is crucial for the studies of extrasolar planet orbiting M-dwarfs, since properties of the host star are directl related to understanding the planet properties and possibl habitability. Understanding of the statistical properties of the dwar stars is also crucial for the Simple Stellar Population models that pla a major role in the modern astrophysics. Hα emission was detected in 33 of the sample with evidence of Hα variability in one objec