A survey for variable young stars with small telescopes: II – mapping a protoplanetary disc with stable structures at 0.15 au

Abstract

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 V1490 Cyg 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 0.02 mag in broad-band filters, allowing detailed investigations into a variety of variability amplitudes over time-scales from hours to several years. Using Gaia DR2, we estimate the distance to the Pelican Nebula to be 870 $^{+70}_{-55}$ pc. V1490 Cyg is a quasi-periodic dipper with a period of 31.447 ± 0.011 d. The obscuring dust has homogeneous properties, and grains larger than those typical in the ISM. Larger variability on short time-scales is observed in U and Rc−H α, with U amplitudes reaching 3 mag on time-scales of hours, indicating that the source is accreting. The H α equivalent width and NIR/MIR colours place V1490 Cyg between CTTS/WTTS and transition disc objects. The material responsible for the dipping is located in a warped inner disc, about 0.15 au 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⊙ yr−1, 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 disc. However, we cannot fully rule out the possibility of an AA Tau-like warp, or occultations by the Hill sphere around a forming planet.

A survey for variable young stars with small telescopes – III. Warm spots on the active star V1598 Cyg

“…Afterwards the colour correction is applied to all stars. In Evitts et al (2020) we have shown that this results in typical photometric uncertainties of the broad band photometry of a few percent. In Fig.…”

“…The star is found near (slightly south) of the sub-cluster 5 identified in the Spitzer/IRAC survey by Guieu et al (2009), but is not listed in their catalogue of YSOs (presumably due to lack of infrared excess, see below). The Gaia DR2 parallax of 2.44 ± 0.02 mas (Gaia Collaboration 2018), places the star at a distance of 405 ± 3 pc (Bailer-Jones et al 2018), whereas IC 5070 has a significantly larger distance, recently estimated as 870 +70 −55 pc (Evitts et al 2020). Thus, V1598 Cyg is a foreground star and does not belong to the star forming region.…”

“…A large fraction of the data is concentrated in a high cadence campaign that was conducted between MJD = 58330 and 58400. This campaign monitored the source V 1490 Cyg in the same field (Evitts et al 2020) but also generated valuable data for V1598 Cyg. During this high cadence period there are 77 measurements in U , 269 in B, 408 in V , 402 in Rc, 66 in Hα, and 210 in Ic.…”

“…The 10, 20 Myr and 1 Gyr, solar metallicity isochrones by Freytag et al (2010) magnitudes are calibrated into a reference system for each of the filters (Froebrich et al 2018). As many of the HOYS images are taken through slightly different filters, we have developed an additional colour correction of the photometry (Evitts et al 2020). This procedure identifies non-variable stars in each HOYS target field and uses their colours and magnitudes to determine colour terms for each individual image.…”

“…While the primary objective of HOYS is 'Hunting Outbursting Young Stars' (as evidenced by the acronym), the project delivers longterm, multi-band optical light curves for many types of variable stars. In a previous paper, we used HOYS light curves to study occultations by circumstellar disk material in the young stellar object V 1490 Cyg (Evitts et al 2020).…”