论文标题
二进制动物园中的独角兽和长颈鹿:与次级伴侣一起剥离的巨人
Unicorns and Giraffes in the binary zoo: stripped giants with subgiant companions
论文作者
论文摘要
我们分析了两个含有巨星的二元系统,即V723 MON(“ Unicorn”)和2M04123153+6738486(“ The Giraffe”)。这两个巨人的轨道更大但较不发光的伴侣,以前被认为是质量间隙黑洞。光谱散开揭示了两个系统中具有星形光谱的发光伴侣。光谱,光曲线和光谱能量分布的联合建模可牢固地约束这两种组成部分的质量,温度和半径:初选是发光的,很酷的巨人($ t _ {\ rm eff,\ \,\ \,giant} = 3,800 22.5 \,r _ {\ odot} $和$ 25 \,r _ {\ odot} $),具有异常低的质量($ m _ {\ rm giant} \ oft 0.4 \,m _ {\ odot} $),可能会填充其Roche lobes。次生仅是稍温暖的子观念($ t _ {\ rm eff,\,\,2} = 5,800 \,\ rm k $和$ 5,150 \,\ rm k $,$ r_2 = 8.3 \,r_2 = 8.3 \,r _ {\ odot} $ and $ 9 \,r _ \ r _ {消除具有相似质量的主序列星($ M_2 \ of 2.8 \,m _ {\ odot} $和$ \ of 1.8 \,m _ {\ odot} $)。在独角兽中,快速旋转模糊了子巨头的光谱线,即使在其主导总光线的波长下,检测到也很具有挑战性。这两个巨人都有表面丰度,指示CNO加工和随后的包膜剥离。两种系统的属性都可以通过二进制演化模型来复制,其中$ 1-2 \,m _ {\ odot} $ primarter剥夺了同伴上升时,它会剥夺。同伴也进化的事实意味着初始质量比非常统一,或者由于快速积聚而暂时膨胀。独角兽和长颈鹿为在形成宽轨道氦白色矮人形成之前的二进制进化相很少见的窗口,最终是包含两个氦白矮人的紧凑型二进制文件。
We analyze two binary systems containing giant stars, V723 Mon ("the Unicorn") and 2M04123153+6738486 ("the Giraffe"). Both giants orbit more massive but less luminous companions, previously proposed to be mass-gap black holes. Spectral disentangling reveals luminous companions with star-like spectra in both systems. Joint modeling of the spectra, light curves, and spectral energy distributions robustly constrains the masses, temperatures, and radii of both components: the primaries are luminous, cool giants ($T_{\rm eff,\,giant} = 3,800\,\rm K$ and $4,000\,\rm K$, $R_{\rm giant}= 22.5\,R_{\odot}$ and $25\,R_{\odot}$) with exceptionally low masses ($M_{\rm giant} \approx 0.4\,M_{\odot}$) that likely fill their Roche lobes. The secondaries are only slightly warmer subgiants ($T_{\rm eff,\,2} = 5,800\,\rm K$ and $5,150\,\rm K$, $R_2= 8.3\,R_{\odot}$ and $9\,R_{\odot}$) and thus are consistent with observed UV limits that would rule out main-sequence stars with similar masses ($M_2 \approx 2.8\,M_{\odot}$ and $\approx 1.8\,M_{\odot}$). In the Unicorn, rapid rotation blurs the spectral lines of the subgiant, making it challenging to detect even at wavelengths where it dominates the total light. Both giants have surface abundances indicative of CNO processing and subsequent envelope stripping. The properties of both systems can be reproduced by binary evolution models in which a $1-2\,M_{\odot}$ primary is stripped by a companion as it ascends the giant branch. The fact that the companions are also evolved implies either that the initial mass ratio was very near unity, or that the companions are temporarily inflated due to rapid accretion. The Unicorn and Giraffe offer a window into into a rarely-observed phase of binary evolution preceding the formation of wide-orbit helium white dwarfs, and eventually, compact binaries containing two helium white dwarfs.