We present the results of an observational campaign for the long-period variable subdwarf B star PG 1338+481. Seven continuous weeks of observing time at the Steward Observatory 1.55 m Kuiper telescope on Mount Bigelow, Arizona, and the 1.3 m MDM telescope at Kitt Peak rendered ~250 hr of simultaneous U/R time series photometry, as well as an extra ~70 hr of R-band-only data. The analysis of the combined light curves resulted in the extraction of 13 convincing periodicities in the 2100-7200 s range, with amplitudes up to ~0.3% and ~0.2% in the U and R, respectively. Comparing the ratios of amplitudes in the two wave bands to those predicted from theory suggests the presence of dipole modes, a notion that is further supported by the period spacing between the highest amplitude peaks. If confirmed, this poses a challenge to current nonadiabatic theory. At the quantitative level, we find that the distribution of the observed period spectrum is highly nonuniform and much sparser than that predicted from a representative model. We provide a possible interpretation in the text. The asteroseismological analysis attempted for PG 1338+481 on the basis of six observed periodicities believed to constitute consecutive dipole modes renders encouraging results. Fixing the effective temperature and surface gravity to the spectroscopic estimates, we successfully isolate just one family of optimal models that can reproduce the measured periods to better than 1%. While the stellar parameters thus inferred must be regarded as preliminary, the achieved fit bodes well for future asteroseismic analyses of long-period variable subdwarf B stars.
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机译：我们提出了对长期变矮型B矮星PG 1338 + 481进行观测活动的结果。在亚利桑那州比奇洛山的Steward天文台1.55 m Kuiper望远镜和在Kitt Peak的1.3 m MDM望远镜连续七个星期的观测时间，使得同时进行U / R时间序列光度测定的时间约为250小时，另外还需要70个小时仅R波段数据。组合光曲线的分析导致提取了2100-7200 s范围内的13个令人信服的周期性，U和R的幅度分别高达〜0.3％和〜0.2％。将两个波段的振幅比与理论预测的振幅比进行比较，就表明存在偶极子模式，最高振幅峰之间的周期间隔进一步支持了这一概念。如果得到证实，这将对当前的非绝热理论构成挑战。在定量水平上，我们发现观察到的周期频谱的分布高度不均匀，并且比从代表性模型预测的稀疏得多。我们在文字中提供了可能的解释。 PG 1338 + 481在六个观察到的周期性（据认为构成连续偶极子模式）的基础上进行的星震分析得出令人鼓舞的结果。将有效温度和地心引力固定到光谱估计值上，我们成功地分离出仅一个家族的最佳模型，该模型可以将测得的周期重现到1％以上。虽然由此推断出的恒星参数必须被视为是初步的，但所获得的拟合对于未来的长周期变矮型B星恒星的星震分析是一个很好的预兆。
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