First stars of the<i>ρ</i>Ophiuchi dark cloud

Pillitteri, I.; Wolk, S. J.; Chen, Hope How-Huan; Goodman, Alyssa A.

doi:10.1051/0004-6361/201628284

Cited by 17 publications

(17 citation statements)

References 58 publications

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“…Two factors can boost the X-ray activity of the hypothetical companion to such a high level: its young age, coeval with ρ Oph and with the other solar-type stars discovered around it (Pillitteri et al 2016), and being part of a tight binary system. This would enhance the stellar activity even more than in a configuration of single star, as observed for example in the RS CVn systems.…”

Section: Discussionmentioning

confidence: 99%

The early B-type star Rho Ophiuchi A is an X-ray lighthouse

Pillitteri

Wolk

Reale

et al. 2017

A&A

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We present the results of a 140 ks XMM-Newton observation of the B2 star ρ Oph A. The star has exhibited strong X-ray variability: a cusp-shaped increase of rate, similar to that which we partially observed in 2013, and a bright flare. These events are separated in time by about 104 ks, which likely corresponds to the rotational period of the star (1.2 days). Time resolved spectroscopy of the X-ray spectra shows that the first event is caused by an increase of the plasma emission measure, while the second increase of rate is a major flare with temperatures in excess of 60 MK (kT ∼ 5 keV). From the analysis of its rise, we infer a magnetic field of ≥ 300 G and a size of the flaring region of ∼ 1.4 − 1.9 × 10 11 cm, which corresponds to ∼ 25% − 30% of the stellar radius. We speculate that either an intrinsic magnetism that produces a hot spot on its surface or an unknown low mass companion are the source of such X-rays and variability. A hot spot of magnetic origin should be a stable structure over a time span of ≥2.5 years, and suggests an overall large scale dipolar magnetic field that produces an extended feature on the stellar surface. In the second scenario, a low mass unknown companion is the emitter of X-rays and it should orbit extremely close to the surface of the primary in a locked spin-orbit configuration, almost on the verge of collapsing onto the primary. As such, the X-ray activity of the secondary star would be enhanced by its young age, and the tight orbit as in RS Cvn systems and ρ Oph would constitute an extreme system that is worthy of further investigation.

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Section: Discussionmentioning

confidence: 99%

The early B-type star Rho Ophiuchi A is an X-ray lighthouse

Pillitteri

Wolk

Reale

et al. 2017

A&A

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“…The latter is mostly located in LCC. As extensively discussed in the literature reviewed by Preibisch and Mamajek (2008), USC is thought to be the youngest part of Sco OB2 (only 22 stars older than 5 Myr were found in the ρ Oph cluster by Pillitteri et al 2016); moreover, star formation in USC has been argued to have been triggered by events (e.g., supernova explosions) in the neighboring UCL region, itself triggered from LCC (the oldest part of Sco OB2). The presence in USC of stars as old as those in LCC does not fit in this picture.…”

Section: Stellar Agesmentioning

confidence: 99%

Stellar population of Sco OB2 revealed by Gaia DR2 data

Damiani

Prisinzano

Pillitteri

et al. 2019

A&A

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Context. The Sco OB2 association is the nearest OB association, extending over approximately 2000 square degrees on the sky. Only its brightest and most massive members are already known (from Hipparcos) across its entire size, while studies of its lower-mass population refer only to small portions of its extent. Aims. In this work we exploit the capabilities of Gaia DR2 measurements to search for Sco OB2 members across its entire size and down to the lowest stellar masses. Methods. We use both Gaia astrometric (proper motions and parallaxes) and photometric measurements (integrated photometry and colors) to select association members, using minimal assumptions derived mostly from the Hipparcos studies. Gaia resolves small details in both the kinematics of individual Sco OB2 subgroups and their distribution with distance from the Sun. Methods are developed to explore the three-dimensional kinematics of a stellar population covering large sky areas. Results. We find nearly 11 000 pre-main sequence members (with less than 3% field-star contamination) of Sco OB2, plus ∼ 3600 main-sequence candidate members with a larger (10-30%) field-star contamination. A higher-confidence subsample of ∼ 9200 premain-sequence (and ∼ 1340 main-sequence) members is also selected (< 1% contamination for the pre-main-sequence), affected however by larger (∼ 15%) incompleteness. We classify separately stars in compact and diffuse populations. Most members belong to one of several kinematically distinct diffuse populations, whose ensemble outlines clearly the shape of the entire association. Upper Sco is the densest region of Sco OB2. It is characterized by a complex spatial and kinematical structure, with no global pattern of motion. Other dense subclusters are found in Upper Centaurus-Lupus (the richest one coincident with the group near V1062 Sco already found by Röser et al. 2018), and in Lower Centaurus-Crux. Most of the clustered stars appear to be younger than the diffuse PMS population, suggesting star formation in small groups which rapidly disperse and dilute, reaching space densities lower than field stars while keeping memory of their original kinematics. We also find that the open cluster IC 2602 has a similar dynamics to Sco OB2, and its PMS members are currently evaporating and forming a diffuse (size ∼ 10 • ) halo around its double-peaked core.

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“…In particular, ρ Oph A is a B2 star in a binary system with another B2 star separated by about 300 AU. The age of this star is estimated in the 7-10 Myr range (Pillitteri et al 2016a), as it is coeval of a group of low mass disk-less stars that surround it. ρ Oph is at the center of a small cluster born from the first burst of star formation in the Rho Ophiuchi cloud.…”

Section: Introductionmentioning

confidence: 99%

Detection of magnetic field in the B2 star ρ Ophiuchi A with ESO FORS2

Pillitteri¹,

Fossati²,

Castro³

et al. 2018

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Circumstantial evidence suggests that magnetism and enhanced X-ray emission are likely correlated in early B-type stars: similar fractions of them (∼ 10%) are strong and hard X-ray sources and possess strong magnetic fields. It is also known that some B-type stars have spots on their surface. Yet up to now no X-ray activity associated with spots on early-type stars was detected. In this Letter we report the detection of a magnetic field on the B2V star ρ Oph A. Previously, we assessed that the X-ray activity of this star is associated with a surface spot, herewith we establish its magnetic origin. We analyzed FORS2 ESO VLT spectra of ρ Oph A taken at two epochs and detected a longitudinal component of the magnetic field of order of ∼ 500 G in one of the datasets. The detection of the magnetic field only at one epoch can be explained by stellar rotation which is also invoked to explain observed periodic X-ray activity. From archival HARPS ESO VLT high resolution spectra we derived the fundamental stellar parameters of ρ Oph A and further constrained its age. We conclude that ρ Oph A provides strong evidence for the presence of active X-ray emitting regions on young magnetized early type stars.

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First stars of theρOphiuchi dark cloud

Cited by 17 publications

References 58 publications

The early B-type star Rho Ophiuchi A is an X-ray lighthouse

The early B-type star Rho Ophiuchi A is an X-ray lighthouse

Stellar population of Sco OB2 revealed by Gaia DR2 data

Detection of magnetic field in the B2 star ρ Ophiuchi A with ESO FORS2

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