LAMOST Reveals Neptune-size Cousins of hot Jupiters, preferentially in "(metal-)rich" and "one-child" Kepler familiesAuthors:Dong et alAbstract:WWe discover a new population of short-period, Neptune-size planets sharing key similarities with hot Jupiters: both populations are preferentially hosted by metal-rich stars, and both are preferentially found in Kepler systems with single transiting planets. We use accurate LAMOST DR4 stellar parameters for main-sequence stars to study the distributions of short-period (1d less than P less than 10d) Kepler planets as a function of host star metallicity. The radius distribution of planets around metal-rich stars is more "puffed up" as compared to that around metal-poor hosts. In two period-radius regimes, planets preferentially reside around metal-rich stars, while there are scantily any planets around metal-poor stars. One is the well-known hot Jupiters, and the other is a new population of Neptune-size planets (2 R_Earth less than R_p less than 6 R_Earth), dubbed as "Hoptunes". Also like hot Jupiters, Hoptunes occur more frequently in systems with single transiting planets than in multiple transiting planetary systems. About 1% of solar-type stars host "Hoptunes", and the frequencies of Hoptunes and hot Jupiters increase with consistent trends as a function of [Fe/H]. In the planet radius distribution, hot Jupiters and Hoptunes are separated by a "valley" at approximately Saturn size (in the range of 6 R_Earth less than approximately R_p less than approximately 10 R_Earth), and this "hot-Saturn valley" represents an approximately order-of-magnitude decrease in planet frequency compared to hot Jupiters and Hoptunes. The empirical "kinship" between Hoptunes and hot Jupiters suggests likely common processes (migration and/or formation) responsible for their existence.