No.346 (#1 – 6)
Molecules with ALMA at Planet-forming Scales (MAPS) XIII: HCO+ and disk ionization structure 1. Youth analysis of near infrared spectra of young low-mass stars and brown dwarfs 2. Quantifying stochasticity-driven uncertainties in H II region metallicities 3. Molecules with ALMA at Planet-forming Scales (MAPS) XI: CN and HCN as Tracers of Photochemistry in Disks 4. Unveiling wide-orbit companions to K-type stars in Sco-Cen with Gaia EDR3 5. Molecules with ALMA at Planet-forming Scales (MAPS). X. Studying deuteration at high angular resolution toward protoplanetary disks 6. 1 Youth analysis of near infrared spectra of young low-mass stars and brown dwarfs V. Almendros-Abad, K. Mužić, A. Moitinho, A. Krone-Martins, K. Kubiak ⋆ We aim at building a method that efficiently identifies young low-mass stars and brown dwarfs from low-resolution near-infrared spectra, by studying gravity- sensitive features and their evolution with age.  We built a dataset composed of all publicly available (~2800) near-infrared spectra of dwarfs with spectral types between M0 and L3. First, we investigate methods for the derivation of the spectral type and extinction using comparison to spectral templates, and various spectral indices.  Then, we examine gravity-sensitive spectral indices and apply machine learning methods, in order to efficiently separate young (≤10 Myr) objects from the field. Using a set of six spectral indices for spectral typing, including two newly defined ones (TLI-J and TLI-K), we are able to achieve a precision below 1 spectral subtype across the entire spectral type range.  We define a new gravity-sensitive spectral index (TLI-g) that consistently separates young from field objects, showing a performance superior to other indices from the literature. Even better separation between the two classes can be achieved through machine learning methods which use the entire NIR spectra as an input. Moreover, we show that the H- and K-bands alone are enough for this purpose. Finally, we evaluate the relative importance of different spectral regions for gravity classification as returned by the machine learning models. We find that the H-band broad-band shape is the most relevant feature, followed by the FeH absorption bands at 1.2 μm and 1.24 μm and the KI doublet at 1.24 μm.近赤外線スペクトルを用いて、低質量星(スペクトル型M0 – L3)の(1)星質量と(2)年齢を求めている。 ● 次世代分光装置(MOONS/VLT, NIRSPEC, NIRISS/JWST)では大規模な分光サンプルを取得する予定であり、従来より効率的な解析手法が求められている。 ●星の質量・年齢にそれぞれsensitiveなスペクトル指標を評価し直す。大規模なスペクトル・データセットに対して適用することで、性能を評価する。 2 Kirkpatrick (2005) ...表面重力に基づく最初の分類Kirkpatrick et al. (2006), Cruz et al. (2009) ...拡張版●   4 gravity classes; δ, γ, β, α = ~1, 10, 100, 1000 [Myr] Allers & Liu (2013; AL13) ...より大規模なサンプルでの星の年代分類●   3 gravity classes: very low gravity (VL-G, ~10 Myr), intermediate (INT-G, ~100 Myr), field (FLD-G)本研究：データセット(2756 spectra)を3つの年代に分類する●  Young (906): t_star ~< 10 Myr ●   Mid-gravity (248): 10 Myr < t_star (~< 100 Myr) ●   Field (1602):若い星のスペクトルフィーチャーを持たない場合本論文では、対象とするスペクトル型をSpT<L3に限定する(データセットに若い星が含まれたのがこのSpTまでだったため)。 3 #2 | Spectral type and extinctionスペクトル型(SpT)指標の条件●   sub-SpTに対して±1エラーに収まる正確性(=傾きの大きさ) ● 重力の影響をうけないこと(gravity-insensitive,後の年齢決定と縮退しない) ● 少なくとも5 sub-typesを分類できる性能があること(SpTの判定範囲) →先行研究の中で合致するものは4つ：H2O, H2O-2, WK, aH2O^K +新たに2つを定義：TLI-K, TLI-J #2 | Youth assessment with spectral indices年代指標●  Young (906): t_star ~< 10 Myr ●   Mid-gravity (248): 10 Myr < t_star (~< 100 Myr) ●   Field (1602):若い星のスペクトルフィーチャーを持たない場合先行研究のindicesより、新たに定義したindex (TLI-g)の方が高性能5
age/gravity分類宇対して4モデルの戒定習を適用。 SVM ... LDA.前に求めたTLIとSpTを与えたPCA+SVM, RF ...スペクトル全体を与えた機械学201 ●  TLI-g: 1.5-1.565 micron 6
7 Unveiling wide-orbit companions to K-type stars in Sco-Cen with Gaia EDR3 Alexander J. Bohn, Christian Ginski, Matthew A. Kenworthy, Eric E. Mamajek, Tiffany Meshkat, Mark J. Pecaut, Maddalena Reggiani, Christopher R. Seay, Anthony G. A. Brown, Gabriele Cugno, Thomas Henning, Ralf Launhardt, Andreas Quirrenbach, Emily L. Rickman, Damien Ségransan ★ Abbreviated. We aim to identify new low-mass companions to young stars using the astrometric measurements provided by the Gaia space mission and com- plementary VLT/SPHERE data. We identify companion candidates from a sample of K-type, pre-main sequence stars in the Scorpius Centaurus association using the early version of the third data release of the Gaia space mission.  Based on the provided positions, proper motions, and magnitudes, we identify all objects within a predefined radius whose differential proper motions are consistent with a gravitationally bound system. We derive companion masses through comparison with evolutionary tracks. For seven identified companion candidates we use additional data collected with VLT/SPHERE and VLT/NACO to assess the i accuracy of the properties of the companions based on Gaia photometry alone.  We identify 110 comoving companions that have a companionship likelihood of more than 95%. We identify ten especially intriguing companions that have masses in the brown dwarf regime down to 20 M 3 up . Our high-contrast imaging data confirm both astrometry and photometric masses derived from Gaia alone.  We discover a new brown dwarf companion, TYC 8252-533-1 B, with a projected separation of approximately 570 au from its Sun-like primary. SED modeling provides a companion mass of 52 ± 17 M Jup . We show that the Gaia database can identify low-mass companions at wide separations from their host stars.  For K-type Sco-Cen members Gaia can detect sub-stellar objects at projected separations larger than 300 au and is sensitivity limited beyond 1,000 au with a lower mass limit down to 20 Mjup. A similar analysis of other star-forming regions could significantly enlarge the sample size of such objects and test formation and evolution theories of planetary systems.大部分が未発見と考えられるwide-orbit companionsを検証する。 ● 星形成過程シナリオの検証：円盤分裂● 特に、低質量量を探したい：褐色矮星(13 – 80M lup)天体：Scorpius-Centaurus association (Sco-Cen)大規模サンプル：Gaia EDR3高解像度観測：Young Suns Exoplanet Survey (YSES) 8
Gaia EDR3
→ Sco-CenのK型前主系列星(459; input sample) →伴星候補のpreselection Input sampleの各ターゲットに対し、物理的距離が1000[au]以内の天体1. 2.視差測定がないor 0.5masを超える不定性のある天体は棄却残りの天体については、視差がホス3.ト天体の視差から20％以下のずれかを確認赤経・赤緯の固有運動が10[km/s]の4.範囲で一致している天体→ 163 companion candidates (CCs) to 142 Sco-Cen members Input sample (青), preselected list (赤) 9主星からのangular sep. – Gバンド等級● 主星のPSF haloにより、主星に近い・暗い伴星は検出できなくなる。 ●   Gray regionはSPHEREのfield of view →主星と伴星を一度に観測可能(後述)主星からの距離–伴星質量●絶対等級と年齢から伴星質量を求める(BT-Settl and MIST models) ）検出限界のため、褐色矮星が見つかるのは>300[pc]のみ色等級図
● 色等級図上で、Sco-Cen系のトラック(tsystem = 15 Myr)と概ね一致●真の3次元距離・速度は分からないのじ、束縛されている可能性を確認する。 2GM 2GM Vproj P = Uproj 2GM r o Vmax (6) | < 1 System can be gravitationally bound or System most likely not gravitationally bound. | ≥ 1 11 #5 |  High-contrast imaging results TYC 8252-533-1 ...伴星(TYC 8252-533-1 B)が褐色矮星と推定● 連星間距離が小さいため、SPHERE field of viewに主星・伴星共に含まれる(左図) ●固有運動より、主星に重力的に束縛されていることを確認(右図) ●   Separation ~ 570 [pc] →主星のデブリ円盤の外側に位置する12
10 candidate BD companions → future follow-up観測を期待13 #1+4+6 | Molecules with ALMA at Planet-forming Scales (MAPS) VIII: HCO+ and disk ionization structure IX: CN and HCN as Tracers of Photochemistry in Disks X: Studying deuteration at high angular resolution toward protoplanetary disks Web : http://alma-maps.info/ 「星・惑星形成」ゼミで紹介中● 2021/10/15 : MAPS特集I ● 2021/11/12 : MAPS特集II 14 Quantifying stochasticity-driven uncertainties in H II region metallicities Raghav Arora, Mark R. Krumholz, Christoph Federrath ★ With the advent of Integral Field Units (IFUs), surveys can now measure metallicities across the discs of nearby galaxies at scales ≤ 100  pc.  At such small scales, many of these regions contain too few stars to fully sample all possible stellar masses and evolutionary states, leading to stochastic fluctuations in the ionising continuum.  The impact of these fluctuations on the line diagnostics used to infer galaxy metallicities is poorly understood. In this paper, we quantify this impact for six most commonly-used diagnostics. We generate stochastic stellar populations for galaxy patches with star formation rates varying over a factor of 1000, compute the nebular emission that results when these stars ionise gas at a wide range of densities, metallicities, and determine how much inferred metallicities vary with fluctuations in the driving stellar spectrum.  We find that metallicities derived from diagnostics that measure multiple ionisation states of their target elements (e.g. electron temperature methods) are weakly affected (variation < 0.1 dex), but that larger fluctuations (～ 0.4 dex) occur for diagnostics that depend on a single ionisation state. Scatter in the inferred metallicity is generally largest at low star formation rate and metallicity, and is larger for more sensitive observations than for shallower ones. The main cause of the fluctuations is stochastic variation in the ionisation state in the nebula in response to the absence of Wolf-Rayet stars, which dominate the production of ≥ 2 – 3 Ryd photons. Our results quantify the trade-off between line brightness and diagnostic accuracy, and can be used to optimise observing strategies for future IFU campaigns. ●近傍銀河の円盤全体の金属量を100[pc]スケールで測定できるようになった。 ●一方で、こうした小さな領域では星の数が少なすぎるため、あらゆる星質量や進化状態を完全に調べることはできず、イオン化連続スペクトルに確率的な揺らぎが生じる。最も一般的に使われている6種類の診断法に対して、この影響を定量的に評価する。