Planet Hunters X: Searching for Nearby Neighbors of 75 Planet and Eclipsing Binary Candidates from the K2 Kepler Extended Mission

We present high-resolution observations of a sample of 75 K2 targets from Campaigns 1-3 using speckle interferometry on the Southern Astrophysical Research (SOAR) telescope and adaptive optics (AO) imaging at the Keck II telescope. The median SOAR $I$-band and Keck $K_s$-band detection limits at 1" were $\Delta m_{I}=4.4$~mag and $\Delta m_{K_s}=6.1$~mag, respectively. This sample includes 37 stars likely to host planets, 32 targets likely to be eclipsing binaries (EBs), and 6 other targets previously labeled as likely planetary false positives. We find nine likely physically bound companion stars within 3" of three candidate transiting exoplanet host stars and six likely EBs. Six of the nine detected companions are new discoveries; one of the six, EPIC 206061524, is associated with a planet candidate. Among the EB candidates, companions were only found near the shortest period ones ($P<3$ days), which is in line with previous results showing high multiplicity near short-period binary stars. This high-resolution data, including both the detected companions and the limits on potential unseen companions, will be useful in future planet vetting and stellar multiplicity rate studies for planets and binaries.Comment: Accepted in A

Planet Hunters. VIII. Characterization of 41 Long-Period Exoplanet Candidates from Kepler Archival Data

The census of exoplanets is incomplete for orbital distances larger than 1 AU. Here, we present 41 long-period planet candidates in 38 systems identified by Planet Hunters based on Kepler archival data (Q0-Q17). Among them, 17 exhibit only one transit, 14 have two visible transits and 10 have more than three visible transits. For planet candidates with only one visible transit, we estimate their orbital periods based on transit duration and host star properties. The majority of the planet candidates in this work (75%) have orbital periods that correspond to distances of 1-3 AU from their host stars. We conduct follow-up imaging and spectroscopic observations to validate and characterize planet host stars. In total, we obtain adaptive optics images for 33 stars to search for possible blending sources. Six stars have stellar companions within 4". We obtain high-resolution spectra for 6 stars to determine their physical properties. Stellar properties for other stars are obtained from the NASA Exoplanet Archive and the Kepler Stellar Catalog by Huber et al. (2014). We validate 7 planet candidates that have planet confidence over 0.997 (3-{\sigma} level). These validated planets include 3 single-transit planets (KIC-3558849b, KIC-5951458b, and KIC-8540376c), 3 planets with double transits (KIC-8540376b, KIC-9663113b, and KIC-10525077b), and 1 planet with 4 transits (KIC-5437945b). This work provides assessment regarding the existence of planets at wide separations and the associated false positive rate for transiting observation (17%-33%). More than half of the long-period planets with at least three transits in this paper exhibit transit timing variations up to 41 hours, which suggest additional components that dynamically interact with the transiting planet candidates. The nature of these components can be determined by follow-up radial velocity and transit observations.Comment: Published on ApJ, 815, 127 Notations of validated planets are changed in accordance with naming convention of NASA Exoplanet Archiv

Analyzing the interaction between state tax incentives and the federal production tax credit for wind power

This study analyzes the potential impact of state tax incentives on the federal production tax credit (PTC) for large-scale wind power projects. While the federal PTC provides critical support to wind plants in the U.S., its so-called ''double-dipping'' provisions may also diminish the value of - or make ineffectual - certain types of state wind power incentives. In particular, if structured the wrong way, state assistance programs will undercut the value of the federal PTC to wind plant owners. It is therefore critical to determine which state incentives reduce the federal PTC, and the magnitude of this reduction. Such knowledge will help states determine which wind power incentives can be the most effective. This research concludes that certain kinds of state tax incentives are at risk of reducing the value of the federal PTC, but that federal tax law and IRS rulings are not sufficiently clear to specify exactly what kinds of incentives trigger this offset. State investment tax credits seem most likely to reduce federal PTC payments; the impact of state production tax credits as well as state property and sales tax incentives is more uncertain. Further IRS rulings will be necessary to gain clarity on these issues. State policymakers can seek such guidance from the IRS. While the IRS may not issue a definitive ''revenue ruling'' on requests from state policymakers, the IRS has in the past been willing to provide general information letters that can provide non-binding clarification on these matters. Private wind power developers, meanwhile, may seek guidance through ''private letter'' rulings

Analyzing the interaction between state tax incentives and the federal production tax credit for wind power

This study analyzes the potential impact of state tax incentives on the federal production tax credit (PTC) for large-scale wind power projects. While the federal PTC provides critical support to wind plants in the U.S., its so-called "double-dipping" provisions may also diminish the value of - or make ineffectual - certain types of state wind power incentives. In particular, if structured the wrong way, state assistance programs will undercut the value of the federal PTC to wind plant owners. It is therefore critical to determine which state incentives reduce the federal PTC, and the magnitude of this reduction. Such knowledge will help states determine which wind power incentives can be the most effective. This research concludes that certain kinds of state tax incentives are at risk of reducing the value of the federal PTC, but that federal tax law and IRS rulings are not sufficiently clear to specify exactly what kinds of incentives trigger this offset. State investment tax credits seem most likely to reduce federal PTC payments; the impact of state production tax credits as well as state property and sales tax incentives is more uncertain. Further IRS rulings will be necessary to gain clarity on these issues. State policymakers can seek such guidance from the IRS. While the IRS may not issue a definitive "revenue ruling" on requests from state policymakers, the IRS has in the past been willing to provide general information letters that can provide non-binding clarification on these matters. Private wind power developers, meanwhile, may seek guidance through "private letter" rulings

Factors driving wind power development in the United States

In the United States, there has been substantial recent growth in wind energy generating capacity, with growth averaging 24 percent annually during the past five years. About 1,700 MW of wind energy capacity was installed in 2001, while another 410 MW became operational in 2002. This year (2003) shows promise of significant growth with more than 1,500 MW planned. With this growth, an increasing number of states are experiencing investment in wind energy projects. Wind installations currently exist in about half of all U.S. states. This paper explores the key factors at play in the states that have achieved a substantial amount of wind energy investment. Some of the factors that are examined include policy drivers, such as renewable portfolio standards (RPS), federal and state financial incentives, and integrated resource planning; as well as market drivers, such as consumer demand for green power, natural gas price volatility, and wholesale market rules

Planet Hunters X: Searching for nearby neighbors of 75 planet and eclipsing binary candidates from the K2 Kepler extended mission

We present high resolution observations of a sample of 75 K2 targets from Campaigns 1-3 using speckle interferometry on the Southern Astrophysical Research (SOAR) telescope and adaptive optics (AO) imaging at the Keck II telescope. The median SOAR $I$-band and Keck $K_s$-band detection limits at 1'' were $\Delta m_{I}=4.4$ mag and $\Delta m_{K_s}=6.1$ mag, respectively. This sample includes 37 stars likely to host planets, 32 targets likely to be EBs, and 6 other targets previously labeled as likely planetary false positives. We find nine likely physically bound companion stars within 3'' of three candidate transiting exoplanet host stars and six likely eclipsing binaries (EB). Six of the nine detected companions are new discoveries, one of them associated with a planet candidate (EPIC 206061524). Among the EB candidates, companions were only found near the shortest period ones (P<3 days), which is in line with previous results showing high multiplicity near short-period binary stars. This high resolution data, including both the detected companions and the limits on potential unseen companions, will be useful in future planet vetting and stellar multiplicity rate studies for planets and binaries