Ultraviolet spectrum of FU Ori and a “Compromise” model of the FUor

Kravtsova, A. S.; Ламзин, С. А.; Errico, L.; Vittone, A. A.

doi:10.1134/s1063773707110060

Cited by 13 publications

(12 citation statements)

References 29 publications

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“…In FU Ori outbursts, the system is totally dominated by the accretion luminosity. The UV spectrum looks very different from a CTTS: It appears to be a superposition of a hot (9000 K), geometrically thick inner disk and a cooler outer component (5000 K), dominated by a dense forest of absorption lines from disk outflows [145,146]. Blue line wing Red line wing Figure 12.…”

Section: Variabilitymentioning

confidence: 99%

The UV Perspective of Low-Mass Star Formation

Schneider¹,

Günther²

2020

Galaxies

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The formation of low-mass (M 2 M ) stars in molecular clouds involves accretion disks and jets, which are of broad astrophysical interest. Accreting stars represent the closest examples of these phenomena. Star and planet formation are also intimately connected, setting the starting point for planetary systems like our own. The ultraviolet (UV) spectral range is particularly suited to study star formation, because virtually all relevant processes radiate at temperatures associated with UV emission processes or have strong observational signatures in the UV. In this review, we describe how UV observations provide unique diagnostics for the accretion process, the physical properties of the protoplanetary disk, and jets and outflows.CTTSs were initially identified as a new class of objects due their optical variability. Very early on, it was realized that they also show signs of enhanced chromospheric activity, i.e., "emission lines resembling those of the solar chromosphere" [2]. These emission lines are superposed on a photospheric spectrum similar to main sequence stars of late spectral type. Initially, the source of emission in excess of a normal photosphere was speculated to be circumstellar or chromospheric in origin [3].The discovery that CTTSs are above and to the right of the main sequence in an HR-diagram demonstrated in conjunction with theoretical work [4], that these objects must be young and, thus, the progenitors of the large main sequence population [5,6]. This notion is corroborated by the presence of strong Li absorption, which requires ∼ 100× the Li abundance of the Sun [e.g. 7]. Because Li is depleted quickly in stellar interiors, the amount of surface lithium decreases with time in convective stars. Therefore, strong Li absorption can only be found in young stars and thus CTTS must be young [e.g. review by 8].Meanwhile the number of peculiarities found in CTTSs grew, but their established youth alone was insufficient to explain those peculiarities and the "mysteries" of CTTSs remained. Many features, like the origin of the "chromospheric emission" remained unexplained, until the early 1980s when a large variety of models were proposed to explain features of CTTSs including envelopes, outflows, infall, and dust disks.Specifically, the "ultraviolet excess" (measured around 3700 Å) and the "blue continuum", which go along with a weakening of photosperic absorption lines due to veiling [9,10], were shown to correlate with the strength of Hα [11,12]. Such a correlation indicates a common origin of both features as observed for chromospheric emission on the Sun. Thus, it was natural to ascribe the excess continuum emission at short wavelengths to a Balmer continuum, i.e., emission following the capture of a free electron by an ionized hydrogen atom. While that finding pinpoints neither the physical origin nor location of the emitting material, it paved the way for explanations involving a suitably tuned chromosphere for producing the observed (Balmer & Ca II H+K) line fluxes in CTTSs. Quantitative mod...

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Section: Variabilitymentioning

confidence: 99%

The UV Perspective of Low-Mass Star Formation

Schneider¹,

Günther²

2020

Galaxies

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“…However, the XSPEC simulations do not take into account factors that could increase the escape probability for soft photons such as inhomogeneous absorption or incomplete occultation of the corona by the disk (Fig. 6 of Kravtsova et al 2007). The best-fit two-component Gaussian model of the soft-band count distribution in the N-S direction (Fig.…”

Section: The Soft X-ray Componentmentioning

confidence: 99%

“…It has also been suggested that FU Ori's disk may have puffed up inner walls ( Fig. 6 of Kravtsova et al 2007) which could increase obscuration of the central star. But, there is not universal agreement on the structure of FU Ori's disk.…”

Section: X-ray Absorptionmentioning

confidence: 99%

CHANDRAREVEALS VARIABLE MULTI-COMPONENT X-RAY EMISSION FROM FU ORIONIS

Skinner

Güdel

Briggs

et al. 2010

ApJ

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FU Orionis is the prototype of a class of eruptive young stars ("FUors") characterized by strong optical outbursts. We recently completed an exploratory survey of FUors using XMM-Newton to determine their X-ray properties, about which little was previously known. The prototype FU Ori and V1735 Cyg were detected. The X-ray spectrum of FU Ori was found to be unusual, consisting of a cool moderately-absorbed component plus a hotter component viewed through an absorption column density that is an order of magnitude higher. We present here a sensitive (99 ks) follow-up X-ray observation of FU Ori obtained at higher angular resolution with Chandra ACIS-S. The unusual multi-component spectrum is confirmed. The hot component is centered on FU Ori and dominates the emission above 2 keV. It is variable (a signature of magnetic activity) and is probably coronal emission originating close to FU Ori's surface viewed through cool gas in FU Ori's strong wind or accretion stream. In contrast, the X-ray centroid of the soft emission below 2 keV is offset 0. ′′ 20 to the southeast of FU Ori, toward the near-IR companion (FU Ori S). This offset amounts to slightly less than half the separation between the two stars. The most likely explanation for the offset is that the companion contributes significantly to the softer X-ray emission below 2 keV (and weakly above 2 keV). The superimposed X-ray contributions from FU Ori and the companion resolve the paradox posed by XMM-Newton of an apparently single X-ray source viewed through two different absorption columns.

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“…This measurement may or may not be applicable to both components of the binary (FU Ori N as well as to FU Ori S) depending on the geometry of the circumstellar and circumbinary material. Independent knowledge of the extinction to FU Ori N is necessary to validate the findings based on accretion disk models (Kravtsova et al 2007;Zhu et al 2007) in which the extinction is either a derived parameter of the models or a required input to them. Understanding the extinction therefore provides helpful insights concerning the nature of the primary (FU Ori) star as well as the geometry of its surroundings, including the companion.…”

mentioning

confidence: 99%

Constraining Mass Ratio and Extinction in the Fu Orionis Binary System With Infrared Integral Field Spectroscopy

Pueyo

Hillenbrand

Vasisht

et al. 2012

ApJ

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We report low resolution near infrared spectroscopic observations of the eruptive star FU Orionis using the Integral Field Spectrograph Project 1640 installed at the Palomar Hale telescope. This work focuses on elucidating the nature of the faint source, located 0.5 south of FU Ori, and identified in 2003 as FU Ori S. We first use our observations in conjunction with published data to demonstrate that the two stars are indeed physically associated and form a true binary pair. We then proceed to extract J and H band spectro-photometry using the damped LOCI algorithm, a reduction method tailored for high contrast science with IFS. This is the first communication reporting the high accuracy of this technique, pioneered by the Project 1640 team, on a faint astronomical source. We use our low resolution near infrared spectrum in conjunction with 10.2 micron interferometric data to constrain the infrared excess of FU Ori S. We then focus on estimating the bulk physical properties of FU Ori S. Our models lead to estimates of an object heavily reddened, A V = 8 − 12, with an effective temperature of ∼ 4000-6500 K . Finally we put these results in the context of the FU Ori N-S system and argue that our analysis provides evidence that FU Ori S might be the more massive component of this binary system.

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Ultraviolet spectrum of FU Ori and a “Compromise” model of the FUor

Cited by 13 publications

References 29 publications

The UV Perspective of Low-Mass Star Formation

The UV Perspective of Low-Mass Star Formation

CHANDRAREVEALS VARIABLE MULTI-COMPONENT X-RAY EMISSION FROM FU ORIONIS

Constraining Mass Ratio and Extinction in the Fu Orionis Binary System With Infrared Integral Field Spectroscopy

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