Cygnus OB2 is the most massive stellar association within 2 kpc from the Sun. Given its large content of massive stars, counting tens of O and 3 WR stars, and thousands of young low mass stars, Cygnus OB2 is the best target to study how massive stars affect the star formation process in the parental cloud and the evolution of nearby protoplanetary disks. I will present the results of our study on the feedback provided by the environment in Cygnus OB2 on disk evolution, combining the X-ray data from the 1.08 Msec Chandra Cygnus OB2 Legacy Project (P.I. J. J. Drake) with an extensive set of optical and infrared data of the association. I will analyze and compare the destructive feedback provided by disk photoevaporation induced by the intense local UV field and close encounters between members of the association, and I will show evidence indicating that disk evolution in an environment similar to Cygnus OB2 is seriously affected by externally induced photoevaporation while close encounters do not provide an important feedback

GUARCELLO, Mario Giuseppe

Cygnus OB2 is the most massive stellar association within 2 kpc from the Sun. Given its large content of massive stars, counting tens of O and 3 WR stars, and thousands of young low mass stars, Cygnus OB2 is the best target to study how massive stars affect the star formation process in the parental cloud and the evolution of nearby protoplanetary disks.
I will present the results of our study on the feedback provided by the environment in Cygnus OB2 on disk evolution, combining the X-ray data from the 1.08 Msec Chandra Cygnus OB2 Legacy Project (P.I. J. J. Drake) with an extensive set of optical and infrared data of the association. I will analyze and compare the destructive feedback provided by disk photoevaporation induced by the intense local UV field and close encounters between members of the association, and I will show evidence indicating that disk evolution in an environment similar to Cygnus OB2 is seriously affected by externally induced photoevaporation while close encounters do not provide an important feedback

Guarcello, Mario

ZENODO

Photoevaporation and close encounters: how the environment around Cygnus~OB2 affects the evolution of protoplanetary disks

OA@INAF - Istituto Nazionale di Astrofisica

2018Publication Year2020-10-13T10:40:07ZAcceptance in OA@INAFPhotoevaporation and close encounters: how the environment around Cygnus OB2 affects the evolution of protoplanetary disksTitleGUARCELLO, Mario GiuseppeAuthors10.5281/zenodo.1892795DOIhttp://hdl.handle.net/20.500.12386/27757HandleMario Giuseppe Guarcello– INAF Osservatorio Astronomico di PalermoJ. J. Drake, N. J. Wright, J. F. Albacete-Colombo, C. Clarke, B. Ercolano, E. Flaccomio, V. Kashyap, G. Micela, T. Naylor, N. Schneider, S. Sciortino, J. S. VinkI LOVE THIS ACRONYMDisks dispersal timescaleMost [Lada & Lada 2003]/some [Krujessen 2012] of stars in our Galaxy form in clusters. Observational clues in disks dispersal timescale is provided by the decline of the fraction of cluster members with disks with the age of the parental cluster.[i.e. Haish+ 2001, Hernandez+ 2007, Mamajek+ 2009, Bell+ 2013Ribas+ 2015]Environment feedback on disks evolutionMost of stellar clusters do not survive longer than 10 Myrs [Lada & Lada2003].This means that typically protoplanetary disks which form in clustersevolve while the central star is still associated with the parentalcluster, which can affect disks evolution.Feedback from massive stars(M > 7 M⊙):•Externally induced disks photoevaporation•Triggering of star formation•Dissipation of protostellarenvelopes•Supernovae explosions and chemical enrichmentFeedback from other cluster members•Close encounters and gravitational interaction• The gas in the disk is heated by incident FUV (6 eV < hν <13.6 eV,   ̴3000K),  and EUV photons (hν > 13.6 eV ,   ̴104K), that ionize and dissociate H2 molecules. A photoevaporating flow of gas from the disk is created by the intense thermal pressure.• Together with viscous accretion, photoevaporation is proposed as the main mechanism for disks dispersal.Bally & Scoville 1982; Johnstone+. 1998, Hollenbach+. 1990, 1994, 2000; Clarke+ 2001, 2011, Alexander+, 2006, 2014; Dullemond+ 2007; Ercolano+ 2008, 2009, 2011; Gorti & Hollenbach 2009; Armitage 2011; Owen et al. 2012; Koepferl+ 2013Disks photoevaporation[O’dell & Wong 1996; Bally et al. 2000]..it looks like the answer is yes:HST observations of proplyds in the Orion Nebula ClusterCan photoevaporation be induced by nearby O stars?1800 AUDissipation timescales for a 0.01 M⊙disk (Mstar= 1 M⊙) illuminated by FUV (in units of G0).In EUV regime disks closer to     0.5 pc to O stars can be dissipated in  <106 yrs [Johnstone+ 1998]Adams+ 2004Photoevaporation in clustersIn Low Mass clusters no feedback is expected. In fact, in  IC 1795 [Roccatagliata+ 2011] and IC 1396 [Barentsen+ 2011] the disk fraction is constant across the clusters.In Intermediate Massive clusters a 10%-15% decline of disk fraction ONLY in the core of the cluster is observed in NGC 6611 [Guarcello+ 2007, 2009, 2010], Pismis 24 [Fang+2012]; NGC 2244 [Balog+ 2007]; NGC 6231[Damiani+ 2016] Disks destruction by photoevaporation in Trapezium-like environments is also proved by N-body simulations [Scally & Clarke 2001] and ALMA observations [σOrionis, Ansdell+ 2017]No feedback is observed in 20 clusters included in the Mystix survey[Richert et al. 2015]MOST OF THE STAR FORMING ENVIRONMENTS IN OUR GALAXY ARE SAFE FOR DISKS EVOLUTIONClose encountersDuring the dynamical evolution of clusters, stars can get very close to each other.It has been proposed that close encounter between a disk-bearing star and another star can have serious consequences on disk evolution [i.e.: Clarke & Pringle 1993, Tamura+ 1998, Zapatero-Osorio+ 2000, Lucas & Roche 2000, Pfalzner+ 2005, 2006, Thies+ 2005, Adams+ 2006]. For instance:In Trapezium-like clusters, in10 Myrs disks can loose between80% and 30% of their initial mass by close encounters [Pfalzner+ 2006]Recent study indicate thatdistant encounter do not haveimpact on angular momentumloss on disks in clusters[Winter+ 2018] Fraction of mass lost from disks in starswith different masses, in a Trapezium-like(black) and Orion-like(grey) cluster• 1.4kpc from the Sun [Rygl+2012];  the next massive association (the Carina Nebula) is more than 1.5 times more distant.• Identified massive stars: 52 O stars  (•)3 Wolf – Rayet stars114 B starsAmong which two O3 stars, a candidate BHG, and various B supergiant [Wright+ 2015]• The unidentified B population is larger [Knodlseder 2000]• Thousands of PMS stars 3-5 Myrs old  [i.e.: Wright & Drake 2009]Combined r (blue); Hα (green); 8.0µm (red) CygOB2 is the best target in our Galaxy to study large scale star formation in presence of massive stars• 1.08 MsecChandra/ACIS-I observation.  [Drake+ 2016]• 36 pointings (30 kseceach)  designed to have constant sensitivity in the central region. [Wright+ 2015]• Estimated completeness 90% at 1 solar mass in the center [Wright+ 2015]• X-ray catalog combined with deep optical and IR data [Guarcello+ 2015][8.0] image around CygOB2 with overplottedthe survey observations • 7924 X-ray sources have been detected and validated  [Wright+ 2014]• 6563 X-ray sources are classified as members using a Naïve Bayes estimate of probability of being member or contaminant  (4246 candidate class III sources) [Kashyap+ 2018, Guarcello+2014]• 1843 stars with disks selected from optical and infrared photometry (439 X-ray sources) [Guarcello+ 2013]• FUV and EUV fluxes emitted by O and WR stars are calculated using published tables [Parravano+ 2003, Martins+ 2005], and projected across the field• The disk fraction is calculated across the field and its correlation with local FUV field, EUV field, and stellar density studiedDisk fraction vs. UV flux fieldDisk fraction is observed to decline from  ̴40% to ≤ 20% as a function of local FUV and EUV fluxesPossible Bias explored• Inside out sequence of star formation• Decrease of sensitivity in OIR images around massive stars• 2D projection effectResults• Age difference of  ̴3 Myrs inner region vs. outskirt required to explain the DF decline. Only ≤1 Myr observed.• The decline of DF is observed selecting members with J< 17, J< 16, J< 15; M> 0.4 M⊙, M> 0.7 M⊙, Fx >25% and 50% quantiles Fxdistribution.• Performed 5000 simulations of the 3D morphology of the association randomly defining the inclination of the branches connecting stars in MSTs. The decline of DF is always observedMass loss rate induced by EUV radiationEUV field calculated across the field and converted into Ṁ using:The resulting Ṁ ranges from  1.5 × 10-8 M⊙ /yr to 3.9 x 10-7 M⊙ /yr.This mass loss results in a total dis-sipation of a 0.05 M⊙ disk in 3.3 and 0.1 Myrs, respectively .For comparison, such mass loss ratesare induced by Ө1 Ori within 0.44 pc.The O-WR population of CygOB2 really creates a hostile environment for disks, so.. .Why do we still observe disks?Adams+ 2010What shields the disks from EUV radiation?• The equation for Ṁ does not account for the attenuation of EUV photons by the intracluster residual material• To have disk lifetime larger by a factor 5 à FEUV must decrease by a factor 25 à a similar extinction can be achieved with Av being about 1 for FUV and 1.4 for EUV [using Cardelli+ 1989] both corresponding to realistic density particles within the association• Cygnus  OB2 is almost clear of gas [Schneider+ 2006] but residual gas still present [Drew+ 2005] and significant dust in the outskirt [Guarcello+ 2013]• Hydrogen column density (both Cygnus Rift and intra-association) larger than 1021 atoms/cm2[Schneider+ 2016], large enough to be opaque to EUV radiation.Conclusions• Environments can impact disks evolution by externally induced disks photoevaporation and close encounters. This feedback is not important in most of the star forming environments in our Galaxy• Cygnus OB2 is the closest massive association to our Sun, being the best target to study star formation in presence of massive stars. • In CygOB2,  disk fraction is observed to decrease as function of the local FUV and EUV fields.• Stellar densities are not high enough to result in significant disks destruction by close encounters.• Mass loss rate by EUV radiation is high enough to destroy disks in few Myrs across the association. Disks can survive only thanks to the attenuation of EUV radiation by intraclustermaterial. 

Photoevaporation and close encounters: how the environment around Cygnus OB2 affects the evolution of protoplanetary disks

NEUROSURGERY ENTHUSIASTIC WOMEN SOCIETY

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Photoevaporation and close encounters: how the environment around Cygnus OB2 affects the evolution of protoplanetary disks

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