Circumstellar disks revealed by<i>H</i>/<i>K</i>flux variation gradients

Núñez, F. Pozo; Haas, Martín; Chini, R.; Ramolla, M.; Westhues, C.; Hodapp, Klaus W.

doi:10.1051/0004-6361/201526107

Cited by 3 publications

(1 citation statement)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, because the Keplerian timescale of the inner disk is orders of magnitude shorter than the time needed for global disk evolution, circumstellar extinction is expected to vary quasi-periodically (Hillenbrand et al 2013;Stauffer et al 2015). (2) Starspots on the stellar photosphere (Guenther & Hessman 1993;Nguyen et al 2009;Pozo Nuñez et al 2015). Magnetic activity within the YSO can trigger cool starspots like sunspots, and the accretion mass flow from the disk through the magnetic field lines may produce accretion "hot spots" near the magnetic poles on the photosphere of the protostar (Hartmann et al 1994).…”

Section: Color-magnitude Diagram and Variability Mechanismsmentioning

confidence: 99%

Photo-Reverberation Mapping of a Protoplanetary Accretion Disk Around a T Tauri Star

Meng

Plavchan

Rieke

et al. 2016

ApJ

View full text Add to dashboard Cite

Theoretical models and spectroscopic observations of newborn stars suggest that protoplantary disks have an inner "wall" at a distance set by the disk interaction with the star. Around T Tauri stars, the size of this disk hole is expected to be on a 0.1 au scale that is unresolved by current adaptive optics imaging, though some modeldependent constraints have been obtained by near-infrared interferometry. Here we report the first measurement of the inner disk wall around a solar-mass young stellar object, YLW 16B in the ρ Ophiuchi star-forming region, by detecting the light-travel time of the variable radiation from the stellar surface to the disk. Consistent time lags were detected on two nights, when the time series in H (1.6 μm) and K (2.2 μm) bands were synchronized while the 4.5 μm emission lagged by 74.5 ± 3.2 s. Considering the nearly edge-on geometry of the disk, the inner rim should be 0.084 au from the protostar on average, with an error of order 0.01 au. This size is likely larger than the range of magnetospheric truncations and consistent with an optically and geometrically thick disk front at the dust sublimation radius at ∼1500 K. The widths of the cross-correlation functions between the data in different wavebands place possible new constraints on the geometry of the disk.

show abstract

Section: Color-magnitude Diagram and Variability Mechanismsmentioning

confidence: 99%

Photo-Reverberation Mapping of a Protoplanetary Accretion Disk Around a T Tauri Star

Meng

Plavchan

Rieke

et al. 2016

ApJ

View full text Add to dashboard Cite

show abstract

Variability of young stellar objects in the Orion nebula

Noroozi,

Chen,

García-Díaz

et al. 2024

A&A

View full text Add to dashboard Cite

The Orion Nebula is one of the best-studied star-forming regions in our Galaxy and provides an ideal laboratory to study the early stages of star formation. Understanding the variability of young stellar objects (YSOs) can provide valuable insights into the underlying physical processes that occur during this crucial phase of stellar evolution. In this context, we have conducted a photometric survey with high temporal resolution of a six-square-degree region centered on NGC\,1980. We used two filters ($R$ and $I$) between 2012 and 2015 with the 15\,cm twin telescope RoBoTT at the Universit\"atssternwarte Bochum in Chile. Our goal is to identify and characterize the variable objects in this sample using a unique observational setup that allows us to obtain high-quality light curves with time sampling on the order of minutes. This is the first time such an intensive ground-based photometric campaign has been conducted in the Orion Nebula. After careful quality control, more than 13000 light curves were produced in either $R$ or $I$; the total number of matched light curves is 11889. The corresponding stars were subsequently matched with the 2MASS point source catalog, resulting in 8197 stars with $I < 16.5$ mag and AAA quality flags. We employed three methods -- amplitude, standard deviation, and the Stetson J index -- to identify variable objects in our sample, successfully classifying 561 stars as variables (irregular, periodic, and quasi-periodic). These stars serve as the foundation for further analysis. We confirmed 456 of these as known pre-main-sequence stars through cross-referencing with existing YSO catalogs, supported by spectroscopic and photometric data. The youth of the remaining stars was established based on their optical and infrared color signatures. The period, $P$, could be determined for 147 sources and ranges from 0.2 days to several weeks. The frequency of very short periods ($ < 1$ day) is two to four times higher than reported in previous studies. A significant population (10<!PCT!>) comes primarily from weak-line T Tauri stars, which are characterized by rotation periods of less than 1 day. These results emphasize the advantages of observations with an exceptional time sampling strategy that allows the identification of variability on scales from hours to years.

show abstract

The Host Galaxy Fluxes of Active Galaxy Nuclei Are Generally Overestimated by the Flux Variation Gradient Method

Cai,

Wan,

Cai

et al. 2024

Universe

View full text Add to dashboard Cite

In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but this assumption has been questioned by the intrinsic color variation of quasars and local Seyfert galaxies. Here, using an up-to-date thermal fluctuation model to simulate multi-wavelength AGN variability, we theoretically demonstrate that the FVG method generally overestimates the host galaxy flux; that is, it is more significant for brighter AGN/quasars. Furthermore, we observationally confirm that the FVG method indeed overestimates the host galaxy flux by comparing it to that estimated through other independent methods. We thus caution that applying the FVG method should be performed carefully in the era of time-domain astronomy.

show abstract

Circumstellar disks revealed byH/Kflux variation gradients

Cited by 3 publications

References 27 publications

Photo-Reverberation Mapping of a Protoplanetary Accretion Disk Around a T Tauri Star

Photo-Reverberation Mapping of a Protoplanetary Accretion Disk Around a T Tauri Star

Variability of young stellar objects in the Orion nebula

The Host Galaxy Fluxes of Active Galaxy Nuclei Are Generally Overestimated by the Flux Variation Gradient Method

Contact Info

Product

Resources

About