arXiv:1708.02541v1 [astro-ph.SR] 8 Aug 2017 MNRAS aa Nakagawa Takao vnA Rich A. Evan the in Stars FGK Survey of SEEDS Parameters Stellar Fundamental The ohaSchlieder Joshua ioh Suto Hiroshi hknMiyama Shoken di .Turner L. Edwin aauiKuzuhara Masayuki oooiUsuda Tomonori auiaTakato Naruhisa cetd21 uut8 eevd21 uut7 noiia f original in 7; August 2017 Received 8. August 2017 Accepted aaoiIye Masanori oouiKudo Tomoyuki iaoFukagawa Misato oehC Carson C. Joseph iiAkiyama Eiji uaaHayano Yutaka Krzysztof G. He He lminiak G. Krzysztof © oe l ffiitosaelctdatrtecnlso secti conclusion the after located are affiliations All Note: 07TeAuthors The 2017 000 , 1 – ?? 21)Pern 7Spebr21 oplduigMRSL MNRAS using Compiled 2018 September 17 Preprint (2017) 4 4 yj Suzuki Ryuji , 1 aksJanson Markus , 5 ofagBrandner Wolfgang , onP Wisniewski P. John 5 25 5 aaioHayashi Masahiko , 31 5 4 9 29 ouioKusakabe Nobuhiko , 12 , ioh Terada Hiroshi , 11 aooWatanabe Makoto , ueaeMomose Munetake , 24 , esoNishimura Tetsuo , 8 iaGoto Miwa , hyeMCurrie M Thayne , ueeSerabyn Eugene , ooieTamura Motohide , 21 gis rvosypbihdrslsfraprino u ape The sample. our of portion a methodolo Our for sample. results [ our published for previously age against the and activity, chromospheric .mtlsoe sn OOPC oetatln qiaetwdh an computed widths have Poin equivalent we Apache line parameters, D the extract fundamental and at the to Exoplanets calculate taken ROBOSPECT of to spectra Exploration Using echelle Strategic telescope. the from 3.5m in survey stars b (SEEDS) the G determined aru and have We K, stars. F, host detaile und of their a of requires our properties also constrain basic systems the planetary to of non-detections evolution and and thousands formation detections detected these successfully have Utilizing surveys exoplanet Large ABSTRACT iinly efidteae fms forsml are sample our of most of ages the find we ditionally, h curneo eetdc-oigcmain ihteprope words: the t with Key results companions wide our co-moving utilize of detected will stars. frequency survey of SEEDS the occurrence the of the via meta-analysis imaged chr companions future via stellar stars The older indicators. significantly from age ages robust determine cannot abundances ugiKwon Jungmi , Fe 17 / H hmsHenning Thomas , ] norsml scnitn ihta yia fteSlrneighborhoo Solar the of typical that with consistent is sample our in 4 auioH Takahashi H. Yasuhiro , 19 2 y Kandori Ryo , sas)paeaysses–sas udmna aaees– parameters fundamental stars: – systems planetary (stars:) ao .Grady A. Carol , 5 hita Thalmann Christian , 1 no h paper. the of on 8 4 ihe .McElwain W. Michael ioh .Brandt D. Timothy , ak .Hayashi S. Saeko , 32 22 38 5 r 07Fbur 2 February 2017 orm 26 5 4 ahenOh Daehyeon , ihe .Sitko L. Michael , aoMatsuo Taro , 4 eata Egner Sebastian , ouYamada Toru , ohk .Okamoto K. Yoshiko , u-ciMorino Jun-Ichi , , 22 8 lu .Hodapp W. Klaus , 4 ila .Knapp R. Gillian , 13 , 14 4 23 , 30 , 15 22 39 aoh Mayama Satoshi , 5 a-o Pyo Tae-Soo , lve Guyon Olivier , ihhr Takami Michihiro , eleHebb Leslie , ieiTakami Hideki , 37 33 5 4 aksFeldt Markus , 9 my Moro-Martin Amaya , , ag Tomono Daigo , hli Cargile Phillip , 2 34 u Hashimoto Jun auaSuenaga Takuya , < 6 500 y Abe Lyu , 18 M T ff ef iiIshii Miki , 20 feolnt to-date. exoplanets of y scselrproperties stellar asic rs , , mshrcactivity omospheric u oeta we that note but , nesadn of understanding d lo te fterhost their of rties 16 5 ywscalibrated was gy rtnigo the of erstanding A g , tla n sub- and stellar Observatory’s t T , ( 5 itiuinof distribution g E sswt Sub- with isks , 4 tl l v3.0 file style X 8 ) 7 24 , , , , constrain o v 5 10 , t TGVIT d 36 , , 3 , [ , , 4 Fe 4 .Ad- d. stars: , 4 / , 35 H 27 ] , , , 28 , 2 Rich et al.
1 INTRODUCTION to correlate the observed detections of brown dwarfs and Jovian-mass planets with the properties of their host stars. Since the discovery of the first exoplanet surrounding a Fundamental stellar atmospheric parameters such as ef- Sun-like star (Mayor & Queloz 1995), dedicated planet sur- fective temperature (T ), surface gravity (log g ), and iron eff ( ) veys such as, those utilizing the Kepler Space Telescope abundance ( Fe H ), can be calculated using a variety of [ / ] (Borucki et al. 2009, 2010, 2011), the California Planet well tested and vetted codes. For example, MOOG (Sneden Search (Howard et al. 2010; Wright et al. 2011) and the 1973) utilizes plane-parallel atmospheric models to perform Anglo-Australian Telescope planet search (Tinney et al. Local Thermodynamic Equilibrium spectral analysis or syn- 2001; Butler et al. 2001; Wittenmyer et al. 2014) have ex- thesis, given a set of equivalent widths (EW) measured from panded the number of confirmed exoplanets to-date to more a stellar spectrum and a line list. Spectroscopy Made Easy than 3,000 exoplanets (exoplanets.org). These surveys have ∼ (SME; Valenti & Piskunov 1996; Valenti & Fischer 2005; yielded sufficient numbers of detections to enable correla- Piskunov & Valenti 2017) uses Kurucz (Castelli & Kurucz tions with their host star properties, such as mass and metal- 2004) or MARCS (Gustafsson et al. 2008) atmospheric mod- licity, to better constrain our understanding of how planets els and line data from the Vienna Atomic Line Database form. (VALD; Kupka et al. 1999, 2000; Ryabchikova et al. 1997; A variety of studies have sought to identify trends be- Piskunov et al. 1995) to fit synthesized spectra to observed tween the frequency of exoplanets and a given host star’s spectra. Temperature Gravity microtrubulent Velocity IT- fundamental parameters. Shortly after the first detections of erations (TGVIT; Takeda et al. 2002a, 2005) employs tab- exoplanets, it was recognized that there was a trend between ulated EWs computed from a grid of atmospheric models the occurrence of Jovian-mass exoplanets and their host with varying atmospheric parameters. In this paper, we have star metallicity (eg. Gonzalez 1997; Fischer & Valenti 2005). adopted TGVIT to characterize the fundamental properties More recently, this relation has been extended for Jovian- of the SEEDS survey target list. mass planets surrounding intermediate mass sub-giants to We present fundamental atmospheric parameters (Teff , M-dwarf hosts Johnson et al. (2010) and to terrestrial-size log g , Fe H ), microturbulent velocity, chromospheric ac- ( ) [ / ] exoplanets (R<1.7 REarth) (Wang & Fischer 2015). Jovian tivity, and age determinations of the FGK stars in the mass planets are seen to increase in frequency around SEEDS survey. In section 2 we present the observations and their host stars from M-dwarf stars to A-dwarfs stars reduction methods for our echelle spectra. Next, we discuss (Johnson et al. 2010). It has also been suggested that the our methodology for measuring line strengths (section 3.1) frequency of planets varies inversely with the lithium abun- and then using TGVIT (section 3.2) to calculate the fun- dance of the host star (Israelian et al. 2009), though this damental stellar parameters from these line strengths. We trend is still hotly debated (Carlos et al. 2016). These trends compare our analysis with a calibration sample in Section have been identified for planets detected via radial veloc- 3.3. We also discuss the chromospheric activity ages (sec- ity or transit observations; it remains unclear whether such tion 3.4) derived from our spectra. We discuss our results in relationships hold for wide-separation planets detected via Section 4. direct imaging surveys. The majority of exoplanets at small angular separations exhibit correlations with their host stars (e.g. Johnson et al. 2 OBSERVATIONS AND DATA REDUCTION 2010), which is expected from the core accretion forma- tion (Pollack et al. 1996). Since it is unclear whether exo- We observed 110 F,G,K-type stars in the SEEDS master tar- planets detected at wide separation from their host stars get list with the Astrophysical Research Consortium Echelle form via core accretion or disc instability (Boss 2001), it Spectrograph (ARCES) on the Astrophysical Research Con- is critical to robustly characterize the fundamental stellar sortium 3.5 meter telescope at the Apache Point Observa- properties of large direct imaging surveys to better under- tory (APO) (Wang et al. 2003). ARCES provides R 31,500 ˚ ∼ stand the implications and biases of their detection rates. spectra that cover the wavelength range of 3500 A to 10,200 ˚ Partial characterization of the stellar properties of com- A. These observations were made between 2010 October 2 ˚ pleted large planet imaging surveys has been performed to 2016 April 13 at a signal to noise (SNR) at 6000 A rang- (e.g. Nielsen et al. 2008 for VLT/NACO and Biller et al. ing from 83 to 483. Table 1 list the basic properties of our 2013; Nielsen et al. 2013 for Gemini/NICI surveys); and target sample. These data were reduced using standard techniques in will likely occur for ongoing surveys using Gemini GPI 1 (Macintosh et al. 2014) and SPHERE (Beuzit et al. 2008; IRAF. After bias subtraction and flat fielding, the spec- Vigan et al. 2016). The most recent large planet imaging tral orders were extracted. We utilized ThAr lamp exposures survey to be completed is the Strategic Exploration of Ex- taken after each science observation to perform wavelength oplanets and Disks with Subaru (SEEDS) survey (Tamura calibration on these data, and then applied standard helio- 2009; Tamura 2016), whose primary goal was to survey centric velocity corrections. We determined that the wave- ˚ ˚ nearby Solar analogs to search for directly imaged planets length range 4478 A - 6968 A contained a large number of Fe and the discs from which they formed. This survey has an- I and Fe II lines at sufficiently high SNR to extract accurate nounced a number of brown dwarf and exoplanet discov- fundamental stellar parameters. Thus we next continuum eries, including GJ 504 b (Kuzuhara et al. 2013), κ And b (Carson et al. 2013), GJ 758 B (Thalmann et al. 2009), 1 IRAF is distributed by the National Optical Astronomy Obser- Pleiades HII 3441 b (Konishi et al. 2016), and ROXs 42B vatory, which is operated by the Association of Universities for b (Currie et al. 2014). Characterizing the fundamental pa- Research in Astronomy (AURA) under a cooperative agreement rameters of the host stars of this survey will enable one with the National Science Foundation.
MNRAS 000, 1–?? (2017) Stellar Parameters of SEEDS Survey 3 normalized the orders spanning this wavelength range using 3.2 Determining Fundamental Atmospheric continuum in IRAF (Tody 1993, 1986) and a 3rd-4th order Parameters spline function. The orders containing these continuum nor- We used the well established FORTRAN based program malized data were then merged into a single-order spectrum. TGVIT (Takeda et al. 2002a, 2005) to calculate the funda- The systemic velocity for each source (see Table 4) was com- mental atmospheric parameters (T , log g , Fe H ) and puted using an IDL-based program that cross correlated a eff ( ) [ / ] v for our sample. As described in Takeda et al. (2002a), Solar spectrum with each observation. t TGVIT utilizes a tabulated grid of model EWs for Fe I and Fe II lines spanning a range of each of the above fundamen- tal atmospheric parameters and vt . The code uses a downhill simplex methodology with the tabulated model EWs to it- erate to a final set of fundamental stellar parameters for a 3 ANALYSIS spectrum. TGVIT is thus different than SME and MOOG based approaches, which calculate the fundamental atmo- The analysis of our observations of the SEEDS target list spheric parameters for every combination of line strength is aimed at determining the fundamental stellar parameters in a given spectrum. TGVIT adopts three criteria that are for these stars, such as the effective temperature (T ), sur- eff motivated by the effects of the excitation equilibrium, ion- face gravity (log g ), and iron abundance ( Fe H ), as well ( ) [ / ] ization equilibrium, and microturbulence on Fe I and Fe II as the microturbulent velocity correction factor (v ). We also t EWs: compute broad constraints on the age of stars in this sam- 1 - Fe I abundances should not have dependence on the ple, via measurements of chromospheric activity (R ). We HK′ lower excitation potential. utilize TGVIT (Takeda et al. 2002a, 2005), which uses ob- 2 - The abundance derived from Fe I should be equal to served equivalent widths of Fe I and Fe II lines to determine the abundance derived from Fe II. the fundamental stellar parameters, as detailed in Section 3 - The abundances calculated from individual Fe I and 3.1. Our constraints on the ages of these systems is summa- Fe II lines in a given star should not have any dependence rized in Section 3.4. on the EW. As described in detail in Takeda et al. (2002a), these three conditions can be represented by a single dispersion equation (Equation 1). 3.1 Calculating Line Strengths FGK dwarfs have rich absorption spectra in the optical D2 σ2 + σ2 + A A 2 (1) bandpass; hence, determining line strengths for a large num- ≡ 1 2 (h 1i − h 2i) ber of Fe I and Fe II lines in a large sample size is best achieved using some form of automation. We used the C- Condition 2 can be satisfied where the mean abundance based program ROBOSPECT v2.12 (Waters & Hollek 2013) of Fe I ( A ) must equal the mean abundance of Fe II ( A ) h 1i h 2i to determine equivalent widths for absorption lines in our thus A A = 0. Conditions 1 and 3 can be satisfied in h 1i − h 2i sample. ROBOSPECT used a log boxcar function to iden- the same way, where the deviation of the mean abundance tify the local continuum of the normalized spectrum in dis- of A (σ ) and A (σ ) must be minimized. Finally, we h 1i 1 h 2i 2 crete windows, and calculated the SNR in this region. RO- follow Takeda et al. (2005) and restrict our analysis to Fe I BOSPECT identifies absorption lines in the spectrum either and Fe II lines whose EW’s are less than 100 m˚A. via a user supplied line list or by searching for nσ variations Our initial implementation of TGVIT suggested that from the local continuum. The program then fits a functional the best solution could be biased by a few Fe I and Fe II form to those lines to find their EW. lines that exhibited anomalously high or low EWs. To miti- Through an iterative process, we found that we could gate this effect, we implemented a bootstrap method similar achieve qualitative agreement to the observed spectrum by to that used by McCarthy & Wilhelm (2014). Our method using a window size of 40 mA˚ for the local continuum nor- created 150 unique sets of EWs, each of which were com- malization, used 3σ to identify the lines and a gaussian pro- prised of 90% of the original Fe I and Fe II lines measured file to measure the EW values. In addition to a visual inspec- by ROBOSPECT. We found that our choice of initial funda- tion of the synthetic spectrum produced by ROBOSPECT mental parameters did not affect the results, thus we reused compared to the observed spectrum (Figure 1), we also com- the same initial parameter values (T = 5000, log g = 4.0, eff ( ) pared the ROBOSPECT produced EWs versus EWs tabu- vt = 1.0, Fe H = 0.0) for our full sample. [ / ] lated by hand through the use of splot in IRAF. As shown in We ran each of the 150 unique sets of EWs through Figure 2, the EWs determined in an automated fashion via TGIVT. Each TGVIT run computed the best fit param- ROBOSPECT mirror those computed by hand. Note that eters, calculated the EW residuals (EWdata- EWTGVIT ), ROBOSPECT tabulated EWs are available as electronic ta- and identified lines that were > 2.5σ outliers. Next, we re- bles in the online version of this manuscript. We do find a moved the > 2.5σ outlier lines from the input line list. We statistically insignificant offset in the EWs determined via then re-ran TGVIT using the initial parameter values. We these two methods (y intercept offset of -1.2 0.9 m˚A in performed this iterative rejection procedure for a total of 5 ± Figure 2); however, since this offset appears across all of our times per unique set of EWs. Typically, between 5-20 lines calibration sources it suggests the offset might be system- per unique set were removed via this process. Each unique atic and not random noise. As we discuss in Section 4.1, this set of EWs provided a single solution of best fit parameter could lead to an underestimation of Fe H . values. We used the mean of the 150 unique sets to compute [ / ] MNRAS 000, 1–?? (2017) 4 Rich et al. the final solution of fundamental stellar parameter values for (Allende Prieto & Lambert 1999), uvby (Alonso et al. 1996; each star. Olsen 1984), and IR Photometry (Ribas et al. 2003), calcu- We computed uncertainties in our fundamental stel- lated from the wings of Hβ and Mg I b (Fuhrmann 1998), lar parameters in two steps. First, we adopted the statis- and other spectroscopic analysis programs that invoke sim- tical uncertainty calculations within TGVIT described in ilar iterative solution approaches outlined in Heiter & Luck Takeda et al. (2002a). The algorithm took steps away from (2003) and Santos et al. (2004). Takeda et al. (2005) also the converged solution in one parameter at a time until compared TGVIT results to a collection of atmospheric one of the three conditions noted above, and re-expressed parameters for 134 stars compiled from a variety of liter- in equations 2, 3, and 4, was violated. ature sources by Cayrel de Strobel et al. (2001). The off- sets between TGVIT and these literature compilations were determined to be Teff = -39 101 K, log g = 0.00 χmax χmin b < σ (2) ± ( ) ± |( − )× | 1 0.19, and Fe H = -0.05 0.08 (Takeda et al. 2005). More [ / ] ± recently, McCarthy & Wilhelm (2014) found good agree- ment between the atmospheric parameters they derived EWmax EWmin q <σ (3) |( − )× | 1 from TGVIT to those derived from SME (Valenti & Fischer 2005), for a sample of 12 stars. We briefly extend the comparison of TGVIT-derived A A < e + e (4) | h 1i − h 2i| 1 2 atmospheric parameters with those derived via other ap- In the series of inequalities above, the constants b and proaches to calibrate our total line list selection proce- q represent the slope of a linear-regression fit of the abun- dure and test our usage of ROBOSPECT+TGVIT against dance (A1) versus χ and A1 versus EW respectively and the published literature. Specifically, we utilized 8 stars that constants e1 and e2 are the probable error of the abundance were not part of the SEEDS survey, but observed with the (σ √N), where N is the number of lines used to calculate same resolution, SNR, and instrument as used in our sur- / the abundance. The minimum and maximum values for EW vey (ARCES at APO). The first method we used to com- and χ are taken from the line list and the best fit parameter pute fundamental stellar parameters (referred to as BPG solution. To compute the uncertainty of a parameter, one of in Wisniewski et al. 2012) used the 2002 version of MOOG the three parameters (T , log g , vt ) is increased until one (Sneden 1973), the one-dimensional plane-parallel model at- eff ( ) of the three above inequalities (Equations 2, 3, 4) is violated. mospheres interpolated from the ODFNEW grid of ATLAS9 The same parameter is then decreased until it violates one (Castelli & Kurucz 2004), and a line list of 150 Fe I and ∼ of the three above inequalities (Equations 2, 3, 4). The aver- Fe II lines compiled from the Solar Flux Atlas (Kurucz et al. age of the positive and negative differences of the parameter 1984), Utrecht spectral line compilation (Moore et al. 1966), from the best fit value then defines the uncertainty in that and the Vienna Atomic Line Database (Kupka et al. 2000, parameter. This process is then repeated for the other two 1999; Ryabchikova et al. 1997; Piskunov et al. 1995). The parameters. The final uncertainty in the Fe H abundance second method we used to compute these stellar pa- [ / ] was computed by adding the uncertainties in abundance de- rameters (referred to as IAC in Wisniewski et al. 2012) rived from using the accepted range of each of the Teff , also used MOOG Sneden (1973), but with an equivalent log g , vt parameters in quadrature. Note that this method- width line finding program like ROBOSPECT. The third ( ) ology tested the convergence of isolated parameters. While method we used to compute stellar parameters utilized SME McCarthy & Wilhelm (2014) demonstrated that the coupled (Valenti & Piskunov 1996; Valenti & Fischer 2005), follow- uncertainties between the atmospheric parameters were neg- ing the methodology described in Petigura et al. (2017). ligible their analysis was done using spectra of much higher We processed our observations of these 8 stars in the resolution and for only one solar metalicity star. Thus we same manner as our SEEDS target data, measuring line suggest that the errors we determine should be conserva- strengths via ROBOSPECT and computing fundamental tively viewed as lower limits. parameters via TGVIT, as summarized in Section 3.2. The Our use of the bootstrap method allows us to probe fundamental parameters derived via our approach and the how the choice of Fe I and Fe II lines influences the con- three methods described above are plotted in Figure 3 and verged solutions. We calculated the standard deviation of summarized in Table 2. each parameter over the 150 iterations. We then added the To assess the differences between the parameters de- bootstrap-derived uncertainties to the internally computed rived via these three approaches, we fit the data in Figure 3 TGVIT uncertainties in quadrature. We note that this final using the algorithm Orthogonal Distance Regression (ODR) error estimation does not take into account any systematical (Boggs & Rogers 1990) in scipy2, which takes into account errors. uncertainties in both the x and y directions. The mean differ- ences between TGVIT parameters and those derived by the three alternative approaches is < 2σ, as seen in Figure 3. We 3.3 Validating with Calibration Stars do note that there is a clustering of log g values, but these ( ) The fundamental atmospheric properties of stars derived still follow a one-to-one relationship within the errors of the by TGVIT and its precursor program (Takeda et al. 2002a, parameters. These results help demonstrate that our use of 2005) have been robustly compared against a wide va- ROBOSPECT and TGVIT reproduce the atmospheric pa- riety of techniques to compute atmospheric parameters. As detailed in Takeda et al. (2005), TGVIT has been shown to yield similar parameters as those computed from theoretical evolutionary tracks, calculated from B-V 2 https://www.scipy.org/
MNRAS 000, 1–?? (2017) Stellar Parameters of SEEDS Survey 5 rameters derived via MOOG, using the same input dataset, but with different line lists. + = NH NK + We also used these 8 calibration stars to explore SHK α β (7) NV + NR the optimal line identification procedure to use with RO- BOSPECT. Optimizing the line identification procedure is important as unidentified lines effect the placement of the C = 1.13 B V 3 3.91 B V 2 1 ×( − ) − ×( − ) continuum, thus influence the final EW output. Note that + 2.84 B V 0.47 (8) these additional lines identified outside of the Fe I and Fe II ×( − )− line list from Takeda et al. (2005) are only used internally for continuum placement in ROBOSPECT and are not used for C = 4.898 + 1.918 B V 2 2.893 B V 3 (9) subsequent analysis. As noted in Section 3.1, ROBOSPECT 2 − ×( − ) − ×( − ) identifies absorption lines in the spectrum either via a user We measured the strength of the calcium H and K supplied line list or by searching for nσ variations from the emission lines in a 1 Awide˚ band at the line core, follow- local continuum. We found that we were unable to repro- ing Middelkoop (1982). We used regions 20 ˚A-wide centered duce the atmospheric parameters for our 8 calibration stars at 3891 A˚ and 4001 A˚ which are outside of the H and K derived using other codes (Table 2) if we provided no line absorption lines, to measure the local continuum. NV and list to ROBOSPECT. We also noted that using a full line NR are the average of these continuum locations (3891 ˚A list from VALD (Kupka et al. 2000, 1999; Ryabchikova et al. and 4001 A˚ respectively). To compute the normalization 1997; Piskunov et al. 1995) required ROSOSPECT to use (α) and the offset (β) factors, we calibrated our SHK index large computational times. Thus, we used the Fe I and II line (initially with α=1 and β=0) to SHK index values calcu- list from Takeda et al. (2005) and allowed ROBOSPECT to lated by Isaacson & Fischer (2010) for 25 stars in common. automatically additional identify lines by looking for 3 σ Figure 4 compares our measured SHK index to the aver- deviations from the continuum. age SHK index from Isaacson & Fischer (2010); the linear relation determined via use of the ODR fitting algorithm described in subsection 3.3 yielded these normalization and offset factors. Using the correction factor, we calculated the 3.4 Chromospheric Activity Ages final SHK index values, the corresponding RHK′ values, and We computed a measure of chromospheric activity of the resultant ages (see Table 3). Note that Equation 5 from our sample to help constrain their ages. We uti- Mamajek & Hillenbrand (2008) is only valid for log R 10 ( HK′ ) lized the chromospheric activity-age relationship from values between -4.0 and -5.1. The uncertainties quoted in the Mamajek & Hillenbrand (2008), shown in equation 5, where chromospheric-activity ages in Table 3 are propagated from τ is the age of the star in Gyr and RHK′ is the chromospheric the uncertainties in the normalization and offset factors (α activity index. This relationship is based on chromospheric and β). activity levels measured in young stars in clusters, as well as ages for these clusters derived from isochronal fitting. Thus to calculate the ages of our sample stars, we compute the cal- 4 RESULTS cium H and K emission line fluxes (3968.47 A˚ and 3933.66 ˚ We now derive the fundamental atmospheric parameters, A respectively) from our echelle spectra to determine RHK′ . chromospheric activity, and age estimates for our entire sam- ple, outlined in Section 3. Our results for the fundamental = atmospheric parameters are described in Section 4.1. Finally, log τ 38.053 17.912 log RHK′ ( ) − − ( ) we estimate the age of our stars by measuring their chromo- 1.6675 log R 2 (5) − ( HK′ ) spheric activity in Section 4.2.
4.1 Atmospheric Parameter Results RHK′ is defined as the luminosity of the Calcium H and K emission lines divided by the total luminosity of the star. We present our atmospheric parameter results using TGVIT in Table 4. We extracted fundamental parameters for 93 We follow Noyes et al. (1984) and compute RHK′ in Equa- tion 6. Line luminosities, determined by measuring the line stars that had SNR > 50, were non-double-lined spectro- emission flux for the H and K lines, are represented by the scopic binaries, and were well within the Teff parameter grid flux index SHK (Equation 7), where NH and NK are counts of TGVIT. 17 stars could not have their atmospheric param- from the core of the H and K lines, NV and NR are counts eters robustly determined because they were spectroscopic from continuum regions, and α and β are correction fac- binaries (3 sources), they could not have their line strengths tors. We use literature values of each star’s B V magnitude measured with ROBOSPECT (5 sources), they had too low − (see Table 3) to represent the continuum contributing to SNR (4 sources), or TGVIT could not converge on a unique the luminosity of the H and K lines, which is encapsulated solution (5 sources). We noticed that ROBOSPECT failed to fit the continuum between 4478 to 5500 ˚A for a subset in the polynomials C1 (Equation 8; see Noyes et al. 1984). ∼ of early K-type stars. Correspondingly, when data from this The polynomial C2 in Equation 9, adopted from Noyes et al. (1984), encapsulates the total luminosity of the star. spectral range was included in our analysis, the resulting at- mospheric parameters derived from TGVIT did not match previously published literature results. We therefore utilized 4 C C log R = log 1.34 10 SHK 10 1 10 2 (6) a spectral window of 5500 - 6968 A˚ for all early K-type stars 10 ( HK′ ) 10 ( × − − ) MNRAS 000, 1–?? (2017) 6 Rich et al. and used the full spectral window (4478 - 6968 A)˚ for F and For completeness, we also compared the amplitude of G-type stars. We searched for evidence that this reduced our fundamental atmospheric parameters to those derived spectral bandpass biased the stellar parameters by looking via photometric methods in the Geneva-Copenhagen survey at the dispersion of our results as a function of the number of Casagrande et al. (2011), as shown in Figure 6. The offset of Fe II lines used, versus those published by Takeda et al. between our results and those from the Geneva-Copenhagen (2002b, 2005), which also utilizes TGVIT, for the 20 stars survey is within 3σ (0.06 0.03 dex), for common sources. ± common to both surveys, and by Valenti & Fischer (2005), Next, we discuss our atmospheric results for GJ 504, which uses SME for the 49 stars common to both surveys. a G-type star with a directly imaged low-mass companion We identified no differences in the dispersion present, above (Kuzuhara et al. 2013). The age of this system, and hence the 3σ level, between sources whose parameters were de- the inferred mass of its wide companion, is a subject of de- rived from our full spectral windows versus those derived bate in the literature. Kuzuhara et al. (2013) considered a from reduced spectral windows. wide range of techniques to assess the age of the system, It is common to find systematic offsets in the fun- including gyrochronology, chromospheric activity, x-ray ac- damental atmospheric parameters of stars derived via tivity, lithium abundances, and isochrones, and adopted a +350 different methodologies (see e.g. Takeda et al. 2002b; most likely age of 160 60 Myrs. Fuhrmann & Chini (2015) Valenti & Fischer 2005; Prugniel et al. 2007). We explore and D’Orazi et al. (2016− ) have revisited the age estimates the level of these potential offsets in our results, to bet- for GJ 504, and suggested the system has a much older age, ter enable our results to be utilized by future surveys. thereby increasing the inferred mass of the wide compan- We compared the amplitude of our fundamental atmo- ion into the brown dwarf regime. Both Fuhrmann & Chini spheric parameters to those derived via other spectroscopic (2015) and D’Orazi et al. (2016) suggest that GJ 504 might methods (Takeda et al. 2002b, 2005; Valenti & Fischer 2005; have recently engulfed a planetary companion, leading to Prugniel et al. 2007), for an overlapping subset of stars, and the unusual rotation and Li abundances observed. Recent fit a linear relation between them using ODR, as shown in atmospheric modeling by Skemer et al. (2016) is more con- Figure 5. We find that our values of Teff are well matched sistent with a lower-mass interpretation for the wide com- to these previous studies. We find our values of vt are within panion, hence a younger age estimate for the system, al- 3σ of Takeda et al. (2002b; 2005), which is the only spectro- though this work does not exclude the older age hypoth- scopic survey of this group that reports the same flavor of vt esis. The fundamental stellar parameters that we com- as our work. Similarly, although there is dispersion between pute for GJ 504, T 6063 62, log g 4.38 0.13, and eff ± ( ) ± the log g values we derive and those in the literature, these [Fe/H] 0.07 0.05 are within the range of stellar param- ( ) ± differences are within 3σ of the errors (Figure 7). eters for system published by Valenti & Fischer (2005), Our derived Fe H values exhibit minor offsets along Takeda et al. (2007), da Silva et al. (2012), Ram´ırez et al. [ / ] the y-axis shown in Figure 5. Specifically, our Fe H values (2013), Fuhrmann & Chini (2015), and D’Orazi et al. [ / ] are -0.12 0.01 dex smaller than Takeda et al. (2002b, 2005), (2016). The range of stellar parameters for GJ 504 in some ± -0.14 0.01 dex smaller than Valenti & Fischer (2005), and cases exceeds the formal errors quoted for these parameters, ± -0.07 0.02 smaller than Prugniel et al. (2007). The slope likely owing to unrealized calibration offsets between differ- ± of the Fe H offsets is within 2σ of unity (see Figure 5), in- ent analysis techniques. We therefore suggest one needs to [ / ] dicating that the offsets are a simple constant that could be consider the range of determined fundamental stellar param- used to allow one to place our results on the same absolute eters for the system when using these data to determine an scale as each of these literature works. One possible cause age via isochrones. of the systematic offset of Fe H is that ROBOSPECT The distribution of our atmospheric parameters for our [ / ] marginally underestimates EWs as compared to measuring full sample of stars listed is compiled in Table 4. Figure line strengths by-hand, as noted in Section 3. To further ex- 8 shows histograms of our atmospheric parameters: Teff , plore this, we increased the EW values of 4 stars by 1 mA˚ log g , vt , and Fe H . The Teff distribution exhibits a ( ) [ / ] re-ran them through TGVIT, and found an average change fairly uniform distribution across FGK space, whereas vt in Fe H of 0.05. Thus, the marginal underestimation of and log g exhibit peaks that are consistent with main se- [ / ] ( ) line strengths by ROBOSPECT can only partially explain quence stars. Finally, the Fe H distribution of our sample [ / ] these observed offsets. exhibits a roughly gaussian profile around 0.0 dex, consis- Finally, to further explore the magnitude and origin of tent with stars in the solar neighborhood (Casagrande et al. any systematic offsets, we compare the fundamental stellar 2011). parameters we computed for our 8 comparison stars (see Fig- ure 3) to the parameters calculated by Takeda et al. (2002b, 4.2 Chromospheric Activity and Ages 2005), Valenti & Fischer (2005), and Prugniel et al. (2007) (see Figure 5). We find that the slopes and intercepts from We present the chromospheric activity index and associated the 8 sample stars are within 3σ of the slopes and inter- age estimations for our sample in Table 3. 80 of the 112 stars cepts from our sample of stars in common with Takeda et al. in our sample had sufficiently strong Ca II H and K emission (2002b, 2005) Valenti & Fischer (2005), and Prugniel et al. lines and B V Values within the validity range of Eq. 5. − (2007) for the T , log g , and vt parameters. The Fe H to allow us to calculate R values. Our results are con- eff ( ) [ / ] HK′ slopes are also within 3σ of one another; however, the y- sistent with those tabulated by Isaacson & Fischer (2010), intercept offsets computed for the sample of stars in com- Gaidos et al. (2000), and Mishenina et al. (2012) (Figure 9). mon with Takeda et al. (2002b, 2005) and Valenti & Fischer We note that differences from previous published values can (2005) are > 3σ different compared to that from the 8 com- result from adopting different B V values used when cal- − parison stars. culating RHK′ and/or intrinsic variability in the level of a
MNRAS 000, 1–?? (2017) Stellar Parameters of SEEDS Survey 7 star’s chromospheric activity (see e.g. Isaacson & Fischer age is based on a single epoch of chromospheric activity, 2010). We determined ages for 51 stars with RHK′ val- whereas the previous chromospheric activity age calculation ues within limits of the chromospheric activity-age relation is based on 30 years of observations. (Mamajek & Hillenbrand 2008) as shown in Table 3. Figure 10 shows the sample of SEEDS stars for which we were able to derive ages; the majority of the ages 5 CONCLUSION are < 500Myr. Note that this distribution is not indica- tive of the complete age distribution of the SEEDS sur- We have presented the fundamental atmospheric parame- vey, as targets were not selected based on their age. Older ters (T , log g , Fe H ), vt , chromospheric activity, and eff ( ) [ / ] stars (> 1.5 Gyr) are outside of the chromospheric activity- age determinations of a subset the FGK stars in the SEEDS age relation, and thus do not have accurate age estimates survey, based on analysis of high quality, high resolution (Mamajek & Hillenbrand 2008). spectroscopic observations. We demonstrated the reliability It is important to note that while many stars in the of our methodology by comparing a subset of our results SEEDS sample have ages < 500Myr, their determined to those published in the literature. To aid future compar- ages are still too old to distinguish between core accre- ison of our stellar parameter results with those derived us- tion (Pollack et al. 1996) or disk instability (Boss 2001) ing alternate methodologies, we compile offsets for our com- formation scenarios. Planets formed via core accretion are puted Fe H values, (0.06, -0.07, -0.12, -0.14 dex), com- [ / ] thought to loose most of their heat through the accretion pared to the respective literature sources (Casagrande et al. process resulting in ”cold-start” planets (Spiegel & Burrows 2011, Prugniel et al. 2007, Takeda et al. 2002b; 2005, and 2012), while planets formed via disk instability retain a Valenti & Fischer 2005). Finally, we compared our chro- lot of their initial heat resulting in ”hot-start” planets mospheric activity and age determinations to previous (Spiegel & Burrows 2012). One can distinguish ”cold-start” sources (Isaacson & Fischer 2010, Gaidos et al. 2000, and from ”hot-start” directly imaged planets via their thermal Mishenina et al. 2012), and to ages of stars associated with emission up to an age of 100Myr old. While 6 of our stars moving groups with known ages. Our results will aid the in- ∼ have ages < 100Myr (see Table 3), the rest of our sample terpretation of the frequency of wide stellar and sub-stellar have ages that are either too old or inaccurate to distinguish mass companions detected via the SEEDS survey, and com- between cold-start and hot-start formation scenarios for any parison of the results of the SEEDS survey with other high- giant planets they contain Spiegel & Burrows (2012). contrast planet and sub-stellar mass imaging surveys. We compare our computed chromospheric ages for stars in known moving groups against the accepted ages for these moving groups. Mamajek & Hillenbrand (2008) notes a dis- 6 ACKNOWLEDGEMENTS persion for moving group members of 0.25 dex for stars older than 100 Myr and 1 dex for stars less than 100 Myr. The We thank our referee, Ulrike Heiter, for providing construc- chromospheric age we determine for the one star in our sam- tive feedback that improved the content and clarity of this ple (HD 17925; 42 12 Myr) in β Pic Moving Group is manuscript. This work has made use of the VALD database, ± consistent within 2σ with the estimated cluster age of 23 operated at Uppsala University, the Institute of Astronomy ± 3 Myr (Mamajek & Bell 2014). Similarly, the ages for the RAS in Moscow, and the University of Vienna. This research three stars in our sample that are part of the Local Associa- made use of Astropy, a community-developed core Python tion Moving Group, HD 166 (78 28 Myr), HD 37394 (411 package for Astronomy (Astropy Collaboration et al. 2013). ± 142 Myr), and HD 206860 (340 201 Myr), are within 2σ This research has made use of the VizieR catalogue access ± ± of the moving group age of 20-150 Myr (G´alvez-Ortiz et al. tool, CDS, Strasbourg, France. The original description of 2010). The age of our single star located in the Hyades mov- the VizieR service was published in A&AS 143, 23. ing group, V401 Hya (205 95 Myr) is marginally within 1Homer L. Dodge Department of Physics, University of ± the 3σ range of the moving groups age of 50 100 Myr Oklahoma, Norman, OK 73071, USA; [email protected], ± (Brandt & Huang 2015). The largest dispersion in ages for [email protected] our stars within moving groups was found in objects located 2Exoplanets and Stellar Astrophysics Laboratory, Code with the Ursa Major moving group. Although age estimates 667, Goddard Space Flight Center, Greenbelt, MD 20771, of this group range from 200-600 Myr (Eiff et al. 2016 and USA references therein), analysis using MESA models have led to 3Astrobiology Center of NINS, 2-21-1 Osawa, Mitaka, a more recent, precise age of 414 23 Myr (Jones et al. 2015). Tokyo, 181-8588, Japan ± Our ages for HD 43989 (112 58 Myr), HD 63433 (622 4National Astronomical Observatory of Japan, 2-21-1, ± ± 328 Myr), HD 72985 (79 36 Myr), and HD 135599 (29 Osawa, Mitaka, Tokyo, 181-8588, Japan ± 40 Myr) are generally younger than the accepted age of 5Subaru Telescope, National Astronomical Observatory of ± the moving group, although including the 0.25 dex disper- Japan, 650 North A’ohoku Place, Hilo, HI 96720, USA sion in the Mamajek & Hillenbrand (2008) chromospheric 6Institute of Astrophysics and Planetary Sciences, Faculty age relationship brings all of these age estimates within 3-σ of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki agreement except for HD 135599. 310-8512, Japan Finally, we note that our chromospheric age estimate 7Laboratoire Lagrange (UMR 7293), Universite de Nice- from our single observation of GJ 504 (618 390 Myr) is Sophia Antipolis, CNRS, Observatoire de la Cote d’Azur, ± consistent with, albeit less precise than, the previously pub- 28 avenue Valrose, F-06108 Nice Cedex 2, France lished chromospheric age (330 180 Myr; Kuzuhara et al. 8Max Planck Institute for Astronomy, K¨onigstuhl 17, ± 2013). We attribute our lower precision to the fact that our D-69117 Heidelberg, Germany
MNRAS 000, 1–?? (2017) 8 Rich et al.
9Astrophysics Department, Institute for Advanced Study, 36Institute of Astronomy and Astrophysics, Academia Princeton, NJ 08540, USA Sinica, P.O. Box 23-141, Taipei 10617, Taiwan 10Harvard-Smithsonian Center for Astrophysics, 60 Garden 37Institute for Astronomy, ETH Zurich, Wolfgang-Pauli- Street, Cambridge, MA 02138, USA 11Department of Strasse 27, 8093 Zurich, Switzerland Physics and Astronomy, College of Charleston, 58 Coming 38Department of Cosmosciences, Hokkaido University, St., Charleston, SC 29424, USA Kita-ku, Sapporo, Hokkaido 060-0810, Japan 12Graduate School of Science, Osaka University, 1-1 39Astronomical Institute, Tohoku University, Aoba-ku, Machikaneyama, Toyonaka, Osaka 560-0043, Japan Sendai, Miyagi 980-8578, Japan 13Exoplanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center, Greenbelt, MD 20771, USA 14Eureka Scientific, 2452 Delmer, Suite 100, Oakland CA 96002, USA REFERENCES 15Goddard Center for Astrobiology 16Department of Physics, Hobart and William Smith Allende Prieto, C., & Lambert, D. 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MNRAS 000, 1–?? (2017) 10 Rich et al.
Figure 1. This figure plots a sample of HD 172051 spec- trum (black) overploted with the ROBOSPECT model spectrum (green).
Figure 2. This figure plots the EW of HD 172051 measured two different ways. The first with ROBOSPECT (ROBO), the automated line fitting program, and EW measured with SPLOT in IRAF. Note that ROBOSPECT EW values greater than 100 and less than 5 m A˚ were removed from the sample.
MNRAS 000, 1–?? (2017) Stellar Parameters of SEEDS Survey 11
Figure 3. Plots the stellar parameters of the 8 calibration stars listed in Table 2 compared to this work’s stellar parameters. The three methods utilized are colour coated where SME is blue, ARES is yellow, and BPG is green. Each subplot represents a different stellar parameter plotting the one to one line, and the best-fitting line with each y-axis offset labeled in the subfigure.
Figure 4. SH K indices are plotted for Isaacson & Fischer (2010) and our measured SH K values. The SH K indicies are calculated from measured H and K Ca lines fluxes. The S values from Isaacson & Fischer (2010) are an average of multiple observa- tions of the same object to study jitter, which affects the value of SH K that is calculated. We note that our observations have no control for jitter.
MNRAS 000, 1–?? (2017) 12 Rich et al.
Figure 5. The four above panels compare the four fundamental parameters calculated in this work to those calculated in the Takeda et al. (2005, 2007) which has 19 stars in common with our sample (red circles), (Valenti & Fischer 2005) which has 52 stars in common with our sample (blue circles), and ELODIE (Prugniel et al. 2007) which has 27 stars in common with our sample (green circles). The solid black line represents a one-to-one relation between our values and literature values. The coloured dashed lines represent a linear fit to the corresponding literature values, with the parameters of the best fit shown in coloured text. Teff , vt , and Fe H show linear [ / ] relations with previous literature values, and Teff and vt have values consistent with the one-to-one relation. While error bars are not included in this figure due to clarity, Figure 7 shows the distribution of errors for all four of the atmospheric parameters.
Figure 6. Two panels compare the two fundamental parameters calculated in this work to the photometric Copenhagen-Geneva survey (Casagrande et al. 2011) which has 39 stars in common with our sample. The solid black line represents a one-to-one relation between our values and literature values. The coloured dashed lines represent a linear fit to the corresponding literature values, with the parameters of the best fit shown in coloured text.
MNRAS 000, 1–?? (2017) Stellar Parameters of SEEDS Survey 13
Figure 7. Demonstrate the difference between literature values for fundamental stellar parameters and those computed via this manuscript are presented as a function of the uncertainties in these parameters. Takeda et al. (2005, 2007) are the red circles, which has 19 stars in common with our sample. (Valenti & Fischer 2005) are the blue circles, which has 52 stars in common with our sample. The dashed black lines represent 3σ, thus anything to the right of the dashed lines is within 3σ.
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Figure 8. Histograms of the four atmospheric parameters determined for stars in our sample using TGVIT (Table 4); Teff (upper left), log g (upper right), vt (lower left), and Fe H (lower right). ( ) [ / ]
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