This paper is one in a series reporting results from small telescope observations of variable young stars. Here, we study the repeating outbursts of three likely Be stars based on long-term optical, ...near-infrared, and mid-infrared photometry for all three objects, along with follow-up spectra for two of the three. The sources are characterised as rare, truly regularly outbursting Be stars. We interpret the photometric data within a framework for modelling light curve morphology, and find that the models correctly predict the burst shapes, including their larger amplitudes and later peaks towards longer wavelengths. We are thus able to infer the start and end times of mass loading into the circumstellar disks of these stars. The disk sizes are typically 3-6 times the areas of the central star. The disk temperatures are ~40%, and the disk luminosities are ~10% of those of the central Be star, respectively. The available spectroscopy is consistent with inside-out evolution of the disk. Higher excitation lines have larger velocity widths in their double-horned shaped emission profiles. Our observations and analysis support the decretion disk model for outbursting Be stars.
K2 observations of the weak-lined T Tauri binary V928 Tau A+B show the detection of a single, asymmetric eclipse which may be due to a previously unknown substellar companion eclipsing one component ...of the binary with an orbital period \(>\) 66 days. Over an interval of about 9 hours, one component of the binary dims by around 60%, returning to its normal brightness about 5 hours later. From modeling of the eclipse shape we find evidence that the eclipsing companion may be surrounded by a disk or a vast ring system. The modeled disk has a radius of \(0.9923\,\pm\,0.0005\,R_*\), with an inclination of \(56.78\,\pm\, 0.03^\circ\), a tilt of \(41.22\,\pm\,0.05^\circ\), an impact parameter of \(-0.2506\,\pm\,0.0002\,R_*\) and an opacity of 1.00. The occulting disk must also move at a transverse velocity of \(6.637\,\pm\,0.002\,R_*\,\mathrm{day}^{-1}\), which depending on whether it orbits V928 Tau A or B, corresponds to approximately 73.53 or 69.26 \(\mathrm{km s}^{-1}\). A search in ground based archival data reveals additional dimming events, some of which suggest periodicity, but no unambiguous period associated with the eclipse observed by K2. We present a new epoch of astrometry which is used to further refine the orbit of the binary, presenting a new lower bound of 67 years, and constraints on the possible orbital periods of the eclipsing companion. The binary is also separated by 18" (\(\sim\)2250 au) from the lower mass CFHT-BD-Tau 7, which is likely associated with V928 Tau A+B. We also present new high dispersion optical spectroscopy that we use to characterize the unresolved stellar binary.
We report the discovery and characterization of TOI-1759~b, a temperate (400 K) sub-Neptune-sized exoplanet orbiting the M~dwarf TOI-1759 (TIC 408636441). TOI-1759 b was observed by TESS to transit ...on sectors 16, 17 and 24, with only one transit observed per sector, creating an ambiguity on the orbital period of the planet candidate. Ground-based photometric observations, combined with radial-velocity measurements obtained with the CARMENES spectrograph, confirm an actual period of \(18.85019 \pm 0.00014\) d. A joint analysis of all available photometry and radial velocities reveal a radius of \(3.17 \pm 0.10\,R_\oplus\) and a mass of \(10.8 \pm 1.5\,M_\oplus\). Combining this with the stellar properties derived for TOI-1759 (\(R_\star = 0.597 \pm 0.015\,R_\odot\); \(M_\star = 0.606 \pm 0.020\,M_\odot\); \(T_{\textrm{eff}} = 4065 \pm 51\) K), we compute a transmission spectroscopic metric (TSM) value of over 80 for the planet, making it a good target for transmission spectroscopy studies. TOI-1759 b is among the top five temperate, small exoplanets (\(T_\textrm{eq} < 500\) K, \(R_p < 4 \,R_\oplus\)) with the highest TSM discovered to date. Two additional signals with periods of 80 d and \(>\) 200 d seem to be present in our radial velocities. While our data suggest both could arise from stellar activity, the later signal's source and periodicity are hard to pinpoint given the \(\sim 200\) d baseline of our radial-velocity campaign with CARMENES. Longer baseline radial-velocity campaigns should be performed in order to unveil the true nature of this long period signal.
In this paper we address the problem of overdetermined blind separation and localization of several sources, given that an unknown scaled and delayed version of each source contributes to each sensor ...recording. The separation is performed in the time-frequency domain via an Alternating Least Squares (ALS) algorithm coupled with a Vandermonde structure enforcing strategy across the frequency mode. The latter allows to update the delays and scaling factors of each source with respect to all sensors, up to the ambiguities inherent to the mixing model. After convergence, a reference sensor can be chosen to remove these ambiguities and the Time Difference of Arrival (TDOA) estimates can be exploited to localize the sources individually.
Studying rotational variability of young stars is enabling us to investigate a multitude of properties of young star-disk systems. We utilise high cadence, multi-wavelength optical time series data ...from the Hunting Outbursting Young Stars citizen science project to identify periodic variables in the Pelican Nebula (IC5070). A double blind study using nine different period-finding algorithms was conducted and a sample of 59 periodic variables was identified. We find that a combination of four period finding algorithms can achieve a completeness of 85% and a contamination of 30% in identifying periods in inhomogeneous data sets. The best performing methods are periodograms that rely on fitting a sine curve. Utilising GaiaEDR3 data, we have identified an unbiased sample of 40 periodic YSOs, without using any colour or magnitude selections. With a 98.9% probability we can exclude a homogeneous YSO period distribution. Instead we find a bi-modal distribution with peaks at three and eight days. The sample has a disk fraction of 50%, and its statistical properties are in agreement with other similarly aged YSOs populations. In particular, we confirm that the presence of the disk is linked to predominantly slow rotation and find a probability of 4.8\(\times\)10\(^{-3}\) that the observed relation between period and presence of a disk has occurred by chance. In our sample of periodic variables, we also find pulsating giants, an eclipsing binary, and potential YSOs in the foreground of IC5070.
An attempt is made here to revisit structure formation in a proto-stellar cloud during the early phase of evolution. Molecular cloud subjected to a set of various initial conditions in terms of ...initial temperature and amplitude of azimuthal density perturbation is investigated numerically. Special emphasis remained on the analysis of ring and spiral type instabilities that have shown dependence on certain initial conditions chosen for a rotating solar mass cloud of molecular hydrogen. Generally, a star forming hydrogen gas is considered to be initially at 10K. We have found that a possible oscillation around this typical value can affect the fate of a collapsing cloud in terms of its evolving structural properties leading to proto-star formation. We explored the initial temperature range of cloud between 8K to 12K and compared physical properties of each within the first phase of proto-star formation. We suggest that the spiral structures are more likely to form in strongly perturbed molecular cores that initiate their phase of collapse from temperatures below 10K. Whereas, cores with initial temperatures above 10K develop, instead of spiral, a ring type structure which subsequently experiences the fragmentation. A transition from spiral to ring instability can be observed at a typical initial temperature of 10K.
The HOYS citizen science project conducts long term, multifilter, high cadence monitoring of large YSO samples with a wide variety of professional and amateur telescopes. We present the analysis of ...the light curve of V1490Cyg in the Pelican Nebula. We show that colour terms in the diverse photometric data can be calibrated out to achieve a median photometric accuracy of 0.02mag in broadband filters, allowing detailed investigations into a variety of variability amplitudes over timescales from hours to several years. Using GaiaDR2 we estimate the distance to the Pelican Nebula to be 870\(^{+70}_{-55}\)pc. V1490Cyg is a quasi-periodic dipper with a period of 31.447\(\pm\)0.011d. The obscuring dust has homogeneous properties, and grains larger than those typical in the ISM. Larger variability on short timescales is observed in U and R\(_c-\)H\(\alpha\), with U-amplitudes reaching 3mag on timescales of hours, indicating the source is accreting. The H\(\alpha\) equivalent width and NIR/MIR colours place V1490Cyg between CTTS/WTTS and transition disk objects. The material responsible for the dipping is located in a warped inner disk, about 0.15AU from the star. This mass reservoir can be filled and emptied on time scales shorter than the period at a rate of up to 10\(^{-10}\)M\(_\odot\)/yr, consistent with low levels of accretion in other T Tauri stars. Most likely the warp at this separation from the star is induced by a protoplanet in the inner accretion disk. However, we cannot fully rule out the possibility of an AA Tau-like warp, or occultations by the Hill sphere around a forming planet.
NSV 1907, formerly listed as an irregular variable in variability catalogues, was classified as an Algol-type eclipsing binary in the Catalina Surveys Periodic Variable Star Catalogue. We have ...identified NSV 1907 as an ultraviolet (UV) bright source using measurements from the GALEX space telescope and detected obvious out-of-eclipse variability in archival photometric data from the Catalina Sky Survey, which instigated a closer examination of the object. A spectrum and extensive multicolour photometric observations were acquired, from which we deduce that NSV 1907 is a deeply eclipsing, nova-like cataclysmic variable. Apart from the orbital variations (deep eclipses with a period of P ~ 6.63 hours), changes in mean brightness and irregular short-term variability (flickering) were observed. The presence of a secondary minimum at phase phi ~ 0.5 was established, which indicates a significant contribution of the companion star to the optical flux of the system. We find possible evidence for sinusoidal variations with a period of P ~ 4.2 d, which we interpret as the nodal precession period of the accretion disc. No outbursts or VY Scl-like drops in brightness were detected either by the CSS or during our photometric monitoring. Because of its spectral characteristics and the observed variability pattern, we propose NSV 1907 as a new moderately bright long-period SW Sextantis star. Further photometric and spectroscopic observations are encouraged.
The star KIC 8462852 (Boyajian's Star) displays both fast dips of up to 20% on time scales of days, plus long-term secular fading by up to 19% on time scales from a year to a century. We report on ...CCD photometry of KIC 8462852 from 2015.75 to 2018.18, with 19,176 images making for 1,866 nightly magnitudes in BVRI. Our light curves show a continuing secular decline (by 0.023 +- 0.003 mags in the B-band) with three superposed dips with duration 120-180 days. This demonstrates that there is a continuum of dip durations from a day to a century, so that the secular fading is seen to be by the same physical mechanism as the short-duration Kepler dips. The BVRI light curves all have the same shape, with the slopes and amplitudes for VRI being systematically smaller than in the B-band by factors of 0.77 +- 0.05, 0.50 +- 0.05, and 0.31 +- 0.05. We rule out any hypothesis involving occultation of the primary star by any star, planet, solid body, or optically thick cloud. But these ratios are the same as that expected for ordinary extinction by dust clouds. This chromatic extinction implies dust particle sizes going down to ~0.1 micron, suggesting that this dust will be rapidly blown away by stellar radiation pressure, so the dust clouds must have formed within months. The modern infrared observations were taken at a time when there was at least 12.4% +- 1.3% dust coverage (as part of the secular dimming), and this is consistent with dimming originating in circumstellar dust.
We announce the discovery of KELT-23Ab, a hot Jupiter transiting the relatively bright (\(V=10.3\)) star BD+66 911 (TYC 4187-996-1), and characterize the system using follow-up photometry and ...spectroscopy. A global fit to the system yields host-star properties of \(T_{eff}=5900\pm49 K\), \(M_*=0.945^{+0.060}_{-0.054} M_{\odot}\), \(R_*=0.995\pm0.015 R_{\odot}\), \(L_*=1.082^{+0.051}_{-0.048} L_{\odot}\), log\(g_{*}=4.418^{+0.026}_{-0.025}\) (cgs), and \(\left{\rm Fe}/{\rm H}\right=-0.105\pm0.077\). KELT-23Ab is a hot Jupiter with mass \(M_P=0.938^{+0.045}_{-0.042} M_{\rm J}\), radius \(R_P=1.322\pm0.025 R_{\rm J}\), and density \(\rho_P=0.504^{+0.038}_{-0.035}\) g cm\(^{-3}\). Intense insolation flux from the star has likely caused KELT-23Ab to become inflated. The time of inferior conjunction is \(T_0=2458149.40776\pm0.00091~\rm {BJD_{TDB}}\) and the orbital period is \(P=2.255353^{+0.000031}_{-0.000030}\) days. There is strong evidence that KELT-23A is a member of a long-period binary star system with a less luminous companion, and due to tidal interactions, the planet is likely to spiral into its host within roughly a Gyr. This system has one of the highest positive ecliptic latitudes of all transiting planet hosts known to date, placing it near the Transiting Planet Survey Satellite and James Webb Space Telescope continuous viewing zones. Thus we expect it to be an excellent candidate for long-term monitoring and follow-up with these facilities.
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