Metal-poor Stars Observed with the Automated Planet Finder Telescope. III. CEMP-no Stars are the Descendant of Population III Stars
Nour Aldein Almusleh, Ali Taani, Sergen ?zdemir, Maria Rah, Mashhoor A.Al-Wardat, Gang Zhao, Mohammad K. Mardini
aa r X i v : . [ a s t r o - ph . GA ] F e b Received 26 April 2016; Revised 6 June 2016; Accepted 6 June 2016DOI: xxx/xxxx
ARTICLE TYPE
Metal-poor Stars Observed with the Automated Planet FinderTelescope. III. CEMP-no Stars are the Descendant ofPopulation III Stars
Nour Aldein Almusleh | Ali Taani | Sergen Γzdemir | Maria Rah | Mashhoor A.Al-Wardat | Gang Zhao | Mohammad K. Mardini* Department of Physics, Al al-BaytUniversity, Al Mafraq, Jordan Physics Department, Faculty of Science,Al-Balqa Applied University,Jordan Department of Astronomy and SpaceSciences, Ege University, 35100 Bornova,Δ°zmir, Turkey National Astronomical Observatories andKey Laboratory of ComputationalAstrophysics, Chinese Academy ofSciences, 20A Datun Rd., ChaoyangDistrict, Beijing 100012, China Research Institute for Astronomy andAstrophysics of Maragha (RIAAM),University of Maragheh, Maragheh, Iran Department of Applied Physics andAstronomy, University of Sharjah, Sharjah,United Arab Emirates Sharjah Academy for Astronomy, SpaceSciences and Technology, University ofSharjah, Sharjah, United Arab Emirates Key Lab of Optical Astronomy, NationalAstronomical Observatories, ChineseAcademy of Sciences, Beijing 100101,China Institute of Space Sciences, ShandongUniversity, Weihai 264209, China
Correspondence *Mohammad K. Mardini, Key Lab ofOptical Astronomy, National AstronomicalObservatories, Chinese Academy ofSciences, Beijing 100101, China. Email:[email protected]
In this study, we report a probabilistic insight into the stellar mass and supernovae(SNe) explosion energy of the possible progenitors of ο¬ve CEMP-no stars . Thiswas done by a direct comparison between the abundance ratios [X/Fe] of the light-elements and the predicted nucleosynthetic yields of SN of high-mass metal-freestars. This comparison suggests possible progenitors with stellar mass range of 11 -22 M β and explosion energies of . . erg. The coupling of the chemicalabundances with kinematics derived from πΊπππ
DR2 suggests that our sample donot enter the outer-halo region. In addition, we suggest that these CEMP-no stars are not
πΊπππ -Sausage nor
πΊπππ -Sequoia remnant stars, but another accretion eventmight be responsible for the contribution of these stars to the Galactic Halo of theMilky-Way.
KEYWORDS:
Galaxy, halo stars, abundances, stars kinematics and dynamics, galaxies structure
Population III (Pop III) stars are formed in metal-free gasclouds, as the hydrogen molecules dominated the cooling process, shortly after the Big Bang (for a selected list see,e.g., Hutchins, 1976; Matsuda, SatΒ―o, & Takeda, 1969; Silk,1977a, 1977b; Yoneyama, 1972; Yoshii & Sabano, 1979).In comparison with nowadays stars, Pop III are believed tobe very massive, very luminous, short-lived, and responsi-ble for the production of the very ο¬rst metals. Therefore, it
Nour
ET AL is widely acknowledged that the Pop III supernova explo-sions (SNe) changed the physical nature of our Galaxyand the early universe forever (Mardini, Placco, & et al.,2020; Mardini, Placco, Taani, Li, & Zhao, 2019;Placco, Santucci, & Yuan, 2020). Thus the next generationof stellar objects (Pop II) are believed to be formed from anon-zero metal cloud and have low mass; thus live very long( βΌ
13 Gyr).The science of Stellar Archaeology is built on two fun-damental points: i) Pop II (the so-called metal-poor) starspreserve in their atmosphere the chemical composition ofthe individual or a few supernovae (SN) yields of the pre-vious Pop III (the so-called Pop III chemical ο¬ngerprint,Mardini, Li, & Placco, 2019; Mardini, Placco, et al., 2019;Placco et al., 2016, 2020) and (ii) the robustness of thederived chemical abundances from the high-resolutionspectroscopic data (e.g., Mardini et al., 2020). Therefore, unevolved metal-poor stars did not alter their atmosphericcomposition and would provide a piece of essential informa-tion about their formation site(s) and the chemical evolution ofthe early Galaxy (see Frebel & Surman, 2020, and referencestherein). Pop II stars are known to be deο¬cient in iron (e.g.,Caο¬au et al., 2011; Starkenburg et al., 2018) and enrichedin alpha elements (e.g., Bonifacio et al., 2009; Cayrel et al.,2004). But, several Pop II stars show other peculiarabundances patterns, such as the carbon-enhancement.Metal-poor stars that show high carbon-to-iron abun-dance ratio are called carbon-enhanced metal-poor(CEMP; see Aoki et al., 2007; Beers & Christlieb, 2005;Placco, Frebel, Beers, & Stancliο¬e, 2014; for more detailsabout the classiο¬cation criteria) stars.
Galactic archaeolo-gists are very interested in CEMP stars since they dominatethe tail of the metal-poor region (with frequency βΌ < β , and might holda diagnostic key to further our understanding of the earlyuniverse. The analysis of CEMP stars, in the literature, con-ο¬rmed the existence of several distinguished heavy-elementpatterns, namely: i) CEMP-s stars ([Ba/Fe] > , [Ba/Eu] > ,and [Eu/Fe] β€ ), which show enrichment of barium (mainlyform by s -process, see Burris et al., 2000), ii) CEMP-r stars([Eu/Fe] > and [Ba/Eu] < ), which show enrichment ofeuropium (mainly form by r -process, see Burris et al., 2000),CEMP-s/r ([Ba/Fe] > , [Ba/Eu] > , and [Eu/Fe] > ) stars,which show enrichment in both barium and europium, iv)CEMP-no ([Ba/Fe] < ) stars, which show no enrichmentin heavy elements. It is notable that a large fraction of theconο¬rmed CEMP stars, in the literature, belong to CEMP-nosub-class (e.g., Mardini, Li, & Placco, 2019; Placco et al., Assuming that no material mixing processes have occurred
Metal-rich stars are mainly found in the Galactic bulgeand the Galactic disk. On the other hand, metal-poor starsare found, generally, in the Galactic halo. Still, all thesecomponents might have contribution from earlier accre-tion events (Hansen et al., 2019; Jean-Baptiste et al., 2017;Mardini et al., 2020) . However, it is worth emphasizing thatthe Galactic halo can contain a signiο¬cant number of in-situstars as well (see Tissera, Beers, Carollo, & Scannapieco,2014, and references therein). More recently, 334 stars, with[Fe/H] < β2 . have been assigned to the galactic thickdisk (Mardini et al. 2021 in prep). These stars have beenreported in other studies (Di Matteo et al., 2020; Sestito et al.,2019). In the era of the second data release of the πΊπππ mission (
πΊπππ
DR2; Gaia Collaboration et al., 2018), sev-eral studies already have investigated the kinematics andchemical abundance patterns of metal-poor stars (e.g.,Mardini, Li, & Placco, 2019; Roederer, Hattori, & Valluri,2018; Taani, Khasawneh, Mardini, Abushattal, & Al-Wardat,2020). In this paper, we perform a chemo-dynamical analysisof ο¬ve CEMP-no stars based on
πΊπππ
DR2 astrometry, galac-tic potential
MWPotential2014 (see Bovy, 2015 for moreinformation), and the action-based galaxy modeling state-of-the-arts (
Agama ; see Vasiliev, 2019). We aim to gain putativeinsight into the origin of CEMP-no stars by focusing on com-prehensive chemo-dynamical (combining the chemistry andmotions) analyses for which likely constrain the assemblyhistory of the Galactic halo.
This is a continuation of the work presented inMardini, Placco, et al. (2019) and Mardini, Li, & Placco(2019) (hereafter Paper I and II).
We refer the reader tomore details about the target selection, chemical abun-dancesβ derivation, and the overall scientiο¬c goals in Paper our
ET AL I and II, which we brieο¬y outline here.
In about 10,000metal-poor candidates were originally identiο¬ed in the thirdrelease of the Large Sky Area Multi-Object Fibre Spectro-scopic Telescope survey (LAMOST; Cui, Zhao, & Chu, 2012;Zhao, Chen, & et al., 2006; Zhao, Zhao, Chu, Jing, & Deng,2012). We extracted these candidates by making a directcomparison between the observed ο¬ux and a synthetic grid,where stars are considered as very metal-poor stars if theobtained [Fe/H] β€ β2 . . Afterward, we obtained and analysedhigh-resolution ( π = 110 , carried out with a slit widthof 0.5 mm) spectra for 13 stars, using the 2.4 m AutomatedPlanet Finder. In Paper I and II, we identiο¬ed and analyzeda new representative sample of CEMP stars (ο¬ve CEMP-no,one CEMP-r, and one CEMP-r/s).We have adopted the light-elements (Z β€ ) abundancesfrom Paper I and Paper II (we refer the reader to Table 4 inboth of papers). The adopted elements are suο¬cient to makea direct comparison with theoretical yields of SNe. Heger etal. Heger & Woosley (2010) computed 16,800 nucleosyntheticyields of SNe of high-mass metal-free stars. The well-knownchi-square matching algorithm has used to determine the bestparameter set. The parameter set includes progenitor massesranging between 10 and 100 solar masses, explosion ener-gies corresponding to those mass interval, and the mixingfactor ( π πππ ). The mixing factor changes from no internalmixing to almost complete mixing. Further details about theparameter space and the model description can be found inHeger & Woosley (2010). The positions ( πΌ, πΏ ), proper motions ( π πΌ πππ πΏ, π πΏ ), andparallaxes ( π ) of our targets are taken from πΊπππ
DR2(Gaia Collaboration et al., 2018).
Deriving an accurate dis-tance from an observed parallax is straightforward as π = 1β π only when π > and π β‘ π π β π β² ,where π π is the reported random uncertainty in par-allax. In this paper, we adopted the distances derivedby the Bayesian approach published in Bailer-Jones(Bailer-Jones, Rybizki, Fouesneau, Mantelet, & Andrae,2018). This approach can be implemented to infer dis-tances for stars with noisy or even negative parallaxes. Finally, we adopted the measured heliocentric velocities inPaper I and II as the line-of-sight velocities.
We adopted the Galactic potential
MWPotential2014 (Bovy, 2015) and the open source library written in C++Action-based galaxy modelling architecture (
Agama ) whichis helpful in calculating the gravitational potential of arbi-trary analytic density proο¬les or N-body models, orbitintegration and analysis, transformations between posi-tion/velocity and action/angle variables (for more details, see Vasiliev 2019).
Collectively, these six-dimensional phasespace coordinates, Galactic potential, along with
Agama aresuο¬cient to investigate the orbital evolution of our samplearound the Milky-Way and to integrate detailed orbital param-eters, derive total orbital energy ( πΈ = (1β2) π£ + Ξ¦( π₯ ) ), andcalculate the three dimensional action ( βπ½ = ( π½ π , π½ π , π½ π§ ) ). Inaddition, we used the apocentric ( π πππ ) and pericentric ( π ππππ )radii to deο¬ne the eccentricity as π = ( π πππ β π ππππ )β( π πππ + π ππππ ) . The collected data is suο¬cient to proceed with our investiga-tion. However, employing Monte-Carlo-sampling is useful togain a probabilistic insight into the possible origin of theseο¬ve CEMP-no stars. Therefore, we used a normal distribution,the observed data (chemical abundances and 6D space coordi-nates), and associated error measurements to generate 10,000realization.
We made a direct comparison between the generated light-element abundances (log π ( π ) ) and the predicted yields fromHeger & Woosley (2010) using the open source STARFIT code to statistically estimate the stellar mass of the possi-ble progenitors of these ο¬ve CEMP-no stars. It is noteworthyto mention that the possible progenitor of J1630+0953 andJ2216+0246 have been considered in paper II. We illustrateour comparison in Figure 1 . On the left panel, we plottedatomic number versus [X/H] . Blue ο¬lled squares representthe adopted chemical abundances and error bars representthe associated uncertainties. Gray lines show the predictedSN patterns that ο¬t the observed abundance and theirtransparency can be used as a means of the pattern rep-etition.
The median value and the median absolute deviation(MAD) are shown in legends. The MAD assess how the dataspread in the value space.In general, we found that a model with a mass of 11.4 M β and a mixing factor of π πππ = 0 . ο¬ts 1,561 out of the10,000 realization . The explosion energy of this possibleprogenitor is . erg. We estimate more massive pro-genitors for the rest of our sample 21.5, 20, 13.4, and 15.8 M β for J1630+0953, J1645+4357, J2216+0246, and J2216+2232,respectively. All model details are summarized in Table 1 .Ishigaki et al. (Ishigaki, Tominaga, Kobayashi, & Nomoto,2018) studied about 200 extremely-metal-poor (EMP) stars.The authors showed that the observed abundance patterns in http://starο¬t.org X refers to diο¬erent light-elements
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ET AL
TABLE 1
Summary of models for our target stars.
Star Mass Explosion energy Mixing Factor Number Density Weight M β Γ10 erg π πππ β % J1529+0804 11.4 0.3 0.063 1561 15.61J1630+0953 21.5 0.3 0.158 9140 91.40J1645+4357 20.0 0.3 0.158 6975 69.75J2216+0246 13.4 1.5 0.000 2235 22.35J2216+2232 15.8 1.8 0.016 4362 43.62those EMP stars provide some clues about the physical prop-erties of Pop III stars and their supernova explosion. Theyconcluded that the vast majority of the progenitors of thoseEMP stars lie in the stellar mass range 15-25 M β . Our com-parison shows that three of our sample stars (J1630+0953,J1645+4357, and J2216+2232) agree well within this stel-lar mass range. Our results suggest that a single SN ejecta ofPop III stars with stellar mass range of 11.4- . M β was mostlikely responsible for the observed light elements patterns ofthese ο¬ve CEMP-no stars. STARFIT support comparison withmultiple SN ejecta, this option did not improve the resulting ο¬t-ting, therefore, we argue that no more than one supernova (theso-called mono-enrichment) might alter the chemical compo-sition of the birth-cloud of our CEMP-no stars.
We considered the known zero-point oο¬set parallax asdescribed in Lindegren, HernΓ‘ndez, & Bombrun (2018). Weuse the sampled astrometric solutions to calculate the Galac-tocentric Cartesian ( π πΊπΆ , π πΊπΆ , π πΊπΆ ) coordinates as follows: π πΊπΆ = π β β ππππ ( π ) πππ ( π ) π πΊπΆ = β ππππ ( π ) π ππ ( π ) π πΊπΆ = ππ ππ ( π ) + π§ β Galactic space-velocity components (
U, V, W ) arecalculated and corrected using the Astropy Galactocen-tric frame package (Price-Whelan, Hogg, & et al., 2018;The Astropy Collaboration, 2013): U positive toward theGalactic center, V positive in the direction of Galactic rotationand W positive toward the north Galactic pole. Then we usedthe angle π = π‘ππ β1 ( π πΊπΆ β π πΊπΆ ) to calculate the cylindricalvelocities components for our targets as follows: π π = π πππ ( π ) + π π ππ ( π ) π π = π π ππ ( π ) β π πππ ( π ) π π = π Here, we assume the newly determined Solar System of Rest(LSR) and the Sun position and velocities (Bennett & Bovy, 2019; Gravity Collaboration, Abuter, Amorim, & BaubΓΆck,2019; Masda et al., 2019; SchΓΆnrich, Binney, & Dehnen,2010; Taani, Abushattal, & Mardini, 2019;Taani, Karino, & et al., 2019) in the Galactic coordinateframe. The Sun located at π§ β = 25 pc, at Galactic distance π β = 8.2 kpc, and with circular velocity π£ β = 232.8 kms β1 .The solar peculiar motion is ( π β , π β , π β ) = (11.1, 12.24,7.25) km s β1 .The orbital properties of J1630+0953 and J2216+0246have been calculated, in Paper II, using MWPotential2014 while the orbital properties of J1529+0804, J1645+4357, andJ2216+2232 were calculated, in Paper I, using stΓ€ckel poten-tial. It is well know that the
MWPotential2014 is shallowercompared to the stΓ€ckel one, resulting slightly diο¬erent orbitalproperties (e.g., the total orbital energy of a star calculatedusing the stΓ€ckel will be lower than the orbital energy calcu-lated with the
MWPotential2014 ). Therefore, for the sake ofconsistency, we re-calculate the orbital properties for the entiresample using the
MWPotential2014 .Based on the criteria discussed in this series (star with totalenergy higher than β0 . km s β2 and at distance π πππ greaterthan 15 kpc), the orbital energy, the minimum distance ( π ππππ )of our sample from the center, the maximum distance ( π πππ ),and the maximum height ( π πππ₯ ) suggest that our stars donot enter the outer-halo region (see Table 2 ). Moreover,CEMP-no abundance signature is commonly observedamong classical dwarf spheroidal galaxies (dSphs) andultra-faint dwarf galaxies (UFDs). The Massive dSphs( π β π β β 10 ) have much higher gas content than theUFDs ( π β π β β 10 ). This mass range is resulting thatdSphs have more extensive star formation events. WhileUFDs experience much more metal-poor star formationenvironments (e.g., Frebel & Bromm, 2012). The UFDsstars are predominantly found at extremely low metallicity,where most halo CEMP-no stars are also found. In general,metal-poor halo is mainly from the accretion of mergingevents compared to the dominant in-situ formation of thehalo at metal-rich end (above [Fe/H] > β1 . ) (Roederer,2009). The elemental abundance ratios along with kinematicsof our sample indicate that these stars might have not been our ET AL TABLE 2
Orbital properties of our sampleStar ID πΈ ( km β s ) π πππ₯ (kpc) π πππ (kpc) π ππππ (kpc) π Distance (kpc) d1 (kpc) ErrorJ1529+0804 β1 . +1 . . β1 . +1 . . β1 . +0 . . β1 . +10 . . β1 . +1 . . πΊπππ -Sausage(Belokurov, Erkal, Evans, Koposov, & Deason, 2018;Haywood et al., 2018; Helmi, Babusiaux, & Koppelman,2018) and the
πΊπππ -Sequoia event(Myeong, Vasiliev, Iorio, Evans, & Belokurov, 2019) mighthelp us to investigate the accretion possibility. Figure 2shows the last 10 periods orbit of our sample, in diο¬erentprojections, integrated in time.Figure 3 shows the action-space map of our sample over-laid with the approximate position of the
πΊπππ -Sausage (bluebox) and the
πΊπππ -Sequoia event (orange box). Our samplestars are denoted by the ο¬lled circles. The squares repre-sent other literature CEMP-no stars adopted from JINAbase(Abohalima & Frebel, 2018). The peak of the metallicity-distribution of
πΊπππ -Sausage ([Fe/H] βΌ β1 . ) and the πΊπππ -Sequoia ([Fe/H] βΌ β1 . ) events suggest that all the CEMP-noare most likely not belonging to these accretion events. Numer-ically, eccentric stars (e βΌ | π½ π β π½ π‘ππ‘ | < . and (J π - J π )/ π½ π‘ππ‘ < β0 . are most likely the πΊπππ -Sausage remnantstars. While less eccentric stars (e βΌ π /J π‘ππ‘ < β0 . and (J π β J π )/J π‘ππ‘ < . are most likely the πΊπππ -Sequoia rem-nant stars (Myeong et al., 2019).
Using these values, threestars might being part of the
πΊπππ -Sausage and sevenstars might being part of the
πΊπππ -Sequoia, however, theextremely low metallicity nature of these stars ([Fe/H] < β3 . ) refrain us from making such a conclusion. While theother CEMP-no are unambiguously do not belong to theseaccretion events . This suggests that if the CEMP-no starsmight have extra-galactic origin, another accretion eventshould be responsible for the adds of CEMP-no stars tothe Galactic halo.
More interestingly, J1630+0953 has morecircular orbit than the rest of our sample but it shows high vari-ance between its J π§ and J π . This might be a unique dynamicalproperties, however, the small sample size precluding any solidopinion. In this study, we carried out a statistical estimation of the stel-lar masses of the progenitors, the phase space coordinates,and orbital backward-time integration of the ο¬ve CEMP-nostars, to investigate the chemo-dynamical evolution of thesestars. We adopted the
MWPotential2014 as a Galactic poten-tial model (see Bovy, 2015 for more information) to integratethe corresponding stellar orbits. As consequent, this work fur-ther our understanding of the underlying physical processesby which our Galaxy evolved. The direct comparison of theobserved atmospheric chemical abundances and the predictedSN yields suggests possible progenitors of our CEMP-no stars(J1630+0953, J1645+4357, J2216+0246, and J2216+2232)with stellar mass span the range of 11-22 M β and explosionenergies of . . erg. In addition, the elemen-tal abundance ratios along with kinematics of our starssuggesting extra-galactic origin, such as a low-mass dwarfgalaxy, and have been accreted at a young cosmic age.Moreover, the action-space map of our sample suggest thatthese CEMP-no stars do not match the numerical criteriaof
πΊπππ -Sausage and
πΊπππ -Sequoia remnant stars, insteadof that, it might be used as a clue that another accretionevent might be responsible for the contribution of theseCEMP-no stars to the Milky-Way. Future observations willprovide crucial information to investigate the accretionscenario for these populations.
ACKNOWLEDGEMENTS
We thank Elisabetta Caο¬au for perceptive and constructivecomments, which led to signiο¬cant improvements in themanuscript. This work was supported by the National Natu-ral Science Foundation of China under grant Nos. 11988101and 11890694, and National Key R&D Program of ChinaNo.2019YFA0405502.This work has made use of data from theEuropean Space Agency (ESA) mission
Gaia ( ), processed by the Gaia
Data Processing and Analysis Consortium (DPAC,
Nour
ET AL ).Funding for the DPAC has been provided by national institu-tions, in particular the institutions participating in the
Gaia
Multilateral Agreement.
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Retrieved from https://doi.org/10.1088%2F1674-4527%2F12%2F7%2F002 doi: our ET AL [ X / H ] J1529+0804 1 2 3 4 5 6 7 8J1529+0804MAD = 0.59Median= 2.605 10 15 20 25 307654321 [ X / H ] J1630+0953 2 3 4 5 6 7 8J1630+0953MAD = 0.52Median= 4.105 10 15 20 25 307654321 [ X / H ] J1645+4357 0 1 2 3 4 5J1645+4357MAD = 0.40Median= 1.555 10 15 20 25 307654321 [ X / H ] J2216+0246 1 2 3 4 5 6 7J2216+0246MAD = 0.52Median= 2.375 10 15 20 25 30
Atomic Number [ X / H ] J2216+2232 1 2 3 4 5 6
Residual
J2216+2232MAD = 0.54Median= 2.54
FIGURE 1
Right panel shows the observed [X/H] abundance ratios of the ο¬ve CEMP-no stars (ο¬lled blue squares) as a functionof atomic number, overlaid with the matched SN models. The best ο¬ts and their properties are discussed in the text. The leftpanel shows the posterior distributions for the mean squared residuals π , of the 10,000 simulations. The median and medianabsolute deviation (mad) are shown in legends. Nour
ET AL β β β β y [ k p c ] J1529+0804 β β β β z [ k p c ] β β β β z [ k p c ] β β z [ k p c ] β β β β β β y [ k p c ] J1630+0953 β β β β β z [ k p c ] β β β β z [ k p c ] β β z [ k p c ] β β β β y [ k p c ] J1645+4357 β β β z [ k p c ] β β β z [ k p c ] β β β z [ k p c ] β β β β y [ k p c ] J2216+0246 β β β β z [ k p c ] β β β β z [ k p c ] β β z [ k p c ] β β x[kpc] β β y [ k p c ] J2216+2232 β β β β z [ k p c ] β β β β z [ k p c ] R xy β β z [ k p c ] FIGURE 2
Orbits of our sample stars integrated in time (color-bar) in
MWPotential2014 . The ο¬rst and second columnsshow π πΊπΆ and π πΊπΆ as a function of π πΊπΆ , respectively. The third and fourth columns show π πΊπΆ as a function of π πΊπΆ and thegalactocentric radius, respectively. The dotted-open circles denotes the current location of our stars in diο¬erent frames. Eachrow represent the orbits of one star (see legends). our ET AL β1.00 β0.75 β0.50 β0.25 0.00 0.25 0.50 0.75 1.00 J Ο /J tot β1.00β0.75β0.50β0.250.000.250.500.751.00 ( J z - J r ) / J t o t E cc e n t r i c i t y FIGURE 3
The action-space-map of our sample colored by their eccentricities. The orange and blue boxes denote the approxi-mate locations of
πΊπππ -Sequoia and