Editorial on the Research Topic Frontiers in astronomy and space sciences: Rising star

Fraix-Burnet, D

Howell, SB

Izmodenov, V

Kanik, I

Kopeikin, SM

Marziani, P

McIntosh, SW

Puzzarini, C

Rengel, M

English

Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna

Editorial: Frontiers in astronomyand space sciences: Rising starsSteve B. Howell1*, Vladislav Izmodenov2, Sergei M. Kopeikin3,Paola Marziani4, Cristina Puzzarini5, Miriam Rengel6,Scott W. McIntosh7, Didier Fraix-Burnet8 and Isik Kanik91NASA Ames Research Center, Moffet Field, CA, United States, 2Space Research Institute (IKI), RussianAcademy of Sciences, Moscow, Russia, 3Department of Physics and Astronomy, University of Missouri,Columbia, MO, United States, 4National Institute for Astrophysics, Astronomical Observatory of Padua,Padua, Italy, 5Department of Chemistry “Giacomo Ciamician”, University of Bologna, Bologna, Italy,6Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany, 7National Center forAtmospheric Research, Boulder, CO, United States, 8Univ. Grenoble Alpes, CNRS, IPAG, Grenoble,France, 9Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United StatesKEYWORDSSeyfert galaxies, AGN, interstellar medium, astrochemistry, exoplanetsEditorial on the Research TopicFrontiers in astronomy and space sciences: Rising starsWe are delighted to present the inaugural Frontiers in Astronomy and Space Sciences“Rising Stars” article collection. This collection showcases the high-quality work ofinternationally recognized researchers in the early stages of their independent careers.All Rising Star researchers were individually nominated by the editors of the Journalin recognition of their potential to influence future directions in their respective fields.The work presented here highlights the diversity of research across the breadth ofastronomy and space sciences and presents advances in theory, experiment, andmethodology, providing applications for compelling problems. New articles will beadded to this collection as they are published. Contributions to “Rising Stars” are byinvitation only.The first “Rising Stars” article collection consists of five manuscripts. Two areextragalactic and discuss narrow-line Seyfert 1 galaxies and the AGN radius-luminosity relation, one paper reports on the lack of detected exoplanet transits forProxima Centauri, and finally, two papers cover topics on gas-phase reactivity in theInterstellar Medium and PO+ detection in the G+.693–0.027 molecular cloud.Extragalactic astronomyIt was soon realized after the discovery of quasars that there is a radio-quiet majoritybehind “quasi stellar radio sources”, optical counterparts of the then-mysterious sourcesdominating the sky in the radio wavebands. Since then the relation between the twoclasses—radio quiet and radio loud active galactic nuclei (AGN)—has remained an openOPEN ACCESSEDITED AND REVIEWED BYIsik Kanik,NASA Jet Propulsion Laboratory (JPL),United States*CORRESPONDENCESteve B. Howell,steve.b.howell@nasa.govSPECIALTY SECTIONThis article was submitted toAstrobiology,a section of the journalFrontiers in Astronomy and SpaceSciencesRECEIVED 11 July 2022ACCEPTED 30 August 2022PUBLISHED 10 October 2022CITATIONHowell SB, Izmodenov V, Kopeikin SM,Marziani P, Puzzarini C, Rengel M,McIntosh SW, Fraix-Burnet D and Kanik I(2022), Editorial: Frontiers in astronomyand space sciences: Rising stars.Front. Astron. Space Sci. 9:991696.doi: 10.3389/fspas.2022.991696COPYRIGHT© 2022 Howell, Izmodenov, Kopeikin,Marziani, Puzzarini, Rengel, McIntosh,Fraix-Burnet and Kanik. This is an open-access article distributed under theterms of the Creative CommonsAttribution License (CC BY). The use,distribution or reproduction in otherforums is permitted, provided theoriginal author(s) and the copyrightowner(s) are credited and that theoriginal publication in this journal iscited, in accordance with acceptedacademic practice. No use, distributionor reproduction is permittedwhich doesnot comply with these terms.Frontiers in Astronomy and Space Sciences frontiersin.org01TYPE EditorialPUBLISHED 10 October 2022DOI 10.3389/fspas.2022.991696issue. The latest developments have ushered the sensitivity ofradio instrumentation in the domain of the μ Jansky, and theyhave considerably complicated the matter, revealing sources thatare endowed with a relativistic jet but that are also very faint,implying the possibility of contamination by circumnuclear orhost Galaxy radio emission, which is ultimately associated withstar formation. Of special interest in this context are the so-calledradio-loud Narrow Line Seyfert 1s (RL NLSy1s) analyzed byJärvelä et al., whose radio-quiet counterpart is a class of AGN thatdrives the correlations of the famed Eigenvector 1 parameterspace and that has been accounted for as a young or rejuvenatedform of nuclear activity (Sulentic et al., 2000). As Järvelä et al. say,NLSy1s are complicated sources, where often an interplaybetween the AGN, the various phenomena related to it, andthe host Galaxy can be seen. As such they, however, offer us anunprecedented view of the early stages of the evolution ofpowerful AGN. RL NLSy1s are rare and low radio powersources; yet, their properties suggest the presence of arelativistic radio jet, even if it is associated with a modestblack hole mass (MBH ~ 106M⊙). Järvelä et al. present a studyof several RL NLSy1s and attempt to unveil their complexity bycomputing radio spectral index maps. According to theseauthors, each source is a case in its own right, but theygenerally fit the scenario of a fledgling nuclear activity. Amore thorough view might eventually emerge from radioobservations covering a wide range of radio frequencies (from100 MHz to 50 GHz) made possible by present-day low-frequency arrays and by new generation high-frequencyreceivers.The paper by Panda presents a comprehensive analysis of theissues associated with the scaling laws between the radius of thebroad line emitting region rBLR of type-1 AGN (Seyfert 1 andquasars) and the luminosity. Following extensive reverberationmapping campaigns, it has become clear that type-1 AGN do notfollow a universal scaling law in the simplest form rBLR ∝ L0.5, asoriginally suggested. The original formulation of this law remainsvalid for only a fraction of type-1 AGN, the ones accreting atmodest rates (Population B; Sulentic et al., 2000). Highlyaccreting sources (Population and extreme Population A;Marziani and Sulentic 2014) present a significant deviation inthe sense that the emitting regions are closer to continuumsources: the higher the dimensionless accretion rate (or theEddington ratio), the closer the emitting region is found. Theimportant result of the Panda analysis is a relation betweenradius and luminosity with a dependence on the Eddington ratio(or an observational proxy) and physical conditions, expressedby the product of ionization parameter and number density (hisEqs 7–10). Photoionization computations and an application ofthe dust sublimation prescription permit the recovery ofinformation on the physical conditions for the emittingregions of the two prototypical sources I Zw 1 (Pop. A) andNGC 5548 (Pop. B) that reproduces their observed emission lineequivalent widths and some line intensity ratios. As discussed bythe author, this is just one step toward a complete, self-consistentmodel of the broad line emitting regions, a daunting task giventheir complexity.ExoplanetsIn a well-honed experiment, Gilbert et al. use high-qualityTESS photometric observations of Proxima Centauri to searchfor planet transits. Proxima Cen is known to have a 1.3 earth-mass planet in an 11 days orbit (Anglada-Escudé et al., 2016) andpossibly at least one additional planet with a longer period(Damasso et al., 2020). The short orbital period planet, in itsclose orbit (0.05 AU), places it within the habitable zone of this Mstar. A number of previous studies (e.g., Kipping et al., 2017; Liet al., 2017) have searched for transits of this short-period planetwithout success. However, the high-value of planetaryatmospheric observations by JWST, for example, provided astrong motivation for the team to redo a detailed search forplanetary transits.Proxima Cen is an active M5.5 star with frequent flaresmaking the light curve highly resistant to finding small planettransits (Thackeray, 1950; MacGregor et al., 2021). Therefore, theauthors developed and used some novel software methods toexamine in detail the light curve of Proxima Cen in search oftransits. While no planet transits were detected for Proxima Cen,this study set stringent limits on transiting planets, particularlythose within the habitable zone.AstrochemistryIn Alessandrini and Melosso, the gas-phase reaction betweenoxirane (c-C2H4O) and the CN radical has been computationallyinvestigated, both considering thermochemistry and kinetics.Such a reaction was thought to offer a feasible pathway to theformation of species with C3H3NOmolecular formula, which is afamily of compounds rather elusive in the interstellar medium.Thermochemistry, studied by means of a double-hybrid densityfunctional, revealed several submerged mechanisms with respectto the reactants energy, with the potential formation of oxazoleand cyanoacetaldehyde. However, kinetics suggest that the mainreaction mechanism is the extraction of an H atom, thus leadingto the 2-oxiranyl radical and hydrogen cyanide (HCN), withcyanoacetaldehyde + H and H2CCN + H2CO being also possiblereaction products characterized by lower rate constants. Theproduction of oxazole is instead negligible due to the presence ofa high energy barrier. In conclusion, in the gas-phase reactionbetween oxirane and the CN radical, the only species belongingto the C3H3NO family whose formation is thermochemical andkinetic feasible is cyanoacetaldehyde. This study also pointed outthat, differently from what is reported in the literature for manycyano-containing molecules, the c-C2H4O + CN reaction doesFrontiers in Astronomy and Space Sciences frontiersin.org02Howell et al. 10.3389/fspas.2022.991696not form the cyano-derivative of the reaction partner(i.e., cyanooxirane), because the nucleophilic attack of the CNradical always leads to ring opening. This result might explainwhy, despite the detection of oxirane and the abundance of CN,astronomical searches for cyanooxirane have been so farunsuccessful.Rivilla et al. reported the first detection of the phosphorusmonoxide ion (PO+) in the interstellar medium. Four differentrotational transitions of this molecule, with two of them free fromcontamination by other species, were found in an unbiased andvery sensitive spectral survey toward the G+0.693–0.027molecularcloud. Assuming local thermodynamic equilibrium conditions, theanalysis of these lines yielded a column density N of (6.0 ± 0.7) ×1011 cm2, which means a molecular abundance with respect tomolecular hydrogen of 4.5 × 10−−12. Interestingly, the authorsfound that the column density of PO+ normalized with respect tothe cosmic abundance of elemental phosphorous is greater thanthose of NO+ and SO+ normalized with respect to N and Selemental abundance by factors of 3.6 and 2.3, respectively. TheN(PO+)/N(PO) ratio was found to be 0.12 ± 0.03, which is morethan one order of magnitude larger than that of N(SO+)/N(SO)and N(NO+)/N(NO), thus indicating that–in the ISM–P is moreefficiently ionized than N and S. These results have been explainedby the fact that in shocked regions with high values of cosmic-rayionization rates such as the G+0.693–0.027 molecular cloud,atomic P is easily formed and then ionized efficiently by cosmicrays, thus leading to P+, which produces PO+ by reacting O2 and/orOH. The cosmic-ray ionization of PO might also contributesignificantly, thus explaining the N(PO+)/N(PO) ratio observed.Author contributionsAll authors listed havemade a substantial, direct, and intellectualcontribution to the work, and approved it for publication.AcknowledgmentsThe Editors wish to thank all the authors and reviewers of thepapers submitted to this Research Topic for their time, carefulwork, and patience. We gratefully acknowledge the assistance ofthe staff in the editorial offices at Frontiers, especially. ElenaFedulova, Alicia Fallows, and Mathew Williams.Conflict of interestThe authors declare that the research was conducted in theabsence of any commercial or financial relationships that couldbe construed as a potential conflict of interest.Publisher’s noteAll claims expressed in this article are solely those of the authorsand do not necessarily represent those of their affiliated organizations,or those of the publisher, the editors and the reviewers. Any productthat may be evaluated in this article, or claim that may be made by itsmanufacturer, is not guaranteed or endorsed by the publisher.ReferencesAnglada-Escudé, G., Amado, P. J., Barnes, J., et al. (2016). A terrestrial planetcandidate in a temperate orbit around Proxima Centauri. Nature 536, 437. doi:10.1038/nature19106Damasso, M., Del Sordo, F., Anglada-Escudé, G., Giacobbe, P., Sozzetti, A.,Morbidelli, A., et al. (2020). A low-mass planet candidate orbiting Proxima Centauriat a distance of 1.5 AU. Sci. Adv. 6, eaax7467. doi:10.1126/sciadv.aax7467Kipping, D. M., Cameron, C., Hartman, J. D., Davenport, J. R. A., Matthews, J. M.,Sasselov, D., et al. (2017). No conclusive evidence for transits of Proxima b inMOSTPhotometry. Astron. J. 153, 93. doi:10.3847/1538-3881/153/3/93Li, Y., Stefansson, G., Robertson, P., Monson, A., Canas, C., and Mahadevan, S.(2017). A candidate transit event around Proxima Centauri. Res. Notes AAS 1, 49.doi:10.3847/2515-5172/aaa0d5MacGregor, M. A., Weinberger, A. J., Loyd, R. O. P., et al. (2021). Discovery of anextremely short duration flare from Proxima Centauri usingmillimeter through far-ultraviolet observations. Astrophysical J. Lett. 911, L25. doi:10.3847/2041-8213/abf14cMarziani, P., and Sulentic, J. W. (2014). Highly accreting quasars: Sampledefinition and possible cosmological implications. Mon. Not. R. Astron. Soc.442, 1211–1229. doi:10.1093/mnras/stu951Sulentic, J. W., Marziani, P., and Dultzin-Hacyan, D. (2000). Phenomenology ofbroad emission lines in active galactic nuclei. Annu. Rev. Astronomy Astrophysics38, 521. doi:10.1146/annurev.astro.38.1.521Thackeray, A. D. (1950). Proxima Centauri. Mon. Notes Astronomical Soc. S.Afr. 9, 9.Frontiers in Astronomy and Space Sciences frontiersin.org03Howell et al. 10.3389/fspas.2022.991696

Editorial: Frontiers in astronomy and space sciences: Rising stars

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