Browsing by Subject "rr-lyrae"

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    Calibrating The Cepheid Period-Luminosity Relation From The Infrared Surface Brightness Technique I. The P-Factor, The Milky Way Relations, And A Universal K-Band Relation
    (2011-10) Storm, Jesper; Gieren, Wolfgang; Fouque, Pascal; Barnes, Thomas G.; Pietrzynski, G.; Nardetto, Nicolas; Weber, M.; Granzer, T.; Strassmeier, K. G.; Barnes, Thomas G.; Nicolas Nardetto
    Aims. We determine period-luminosity relations for Milky Way Cepheids in the optical and near-IR bands. These relations can be used directly as reference for extra-galactic distance determination to Cepheid populations with solar metallicity, and they form the basis for a direct comparison with relations obtained in exactly the same manner for stars in the Magellanic Clouds, presented in an accompanying paper. In that paper we show that the metallicity effect is very small and consistent with a null effect, particularly in the near-IR bands, and we combine here all 111 Cepheids from the Milky Way, the LMC and SMC to form a best relation. Methods. We employ the near-IR surface brightness (IRSB) method to determine direct distances to the individual Cepheids after we have recalibrated the projection factor using the recent parallax measurements to ten Galactic Cepheids and the constraint that Cepheid distances to the LMC should be independent of pulsation period. Results. We confirm our earlier finding that the projection factor for converting radial velocity to pulsational velocity depends quite steeply on pulsation period, p = 1.550-0.186 log(P) in disagrement with recent theoretical predictions. We find PL relations based on 70 MilkyWay fundamental mode Cepheids of M(K) = -3.33(+/- 0.09)(log(P)-1.0)-5.66(+/- 0.03), W(VI) = -3.26(+/- 0.11)(log(P)-1.0)-5.96(+/- 0.04). Combining the 70 Cepheids presented here with the results for 41 Magellanic Cloud Cepheids which are presented in an accompanying paper, we find M(K) = -3.30(+/- 0.06)(log(P) - 1.0) - 5.65(+/- 0.02), W(VI) = -3.32(+/- 0.08)(log(P) - 1.0) - 5.92(+/- 0.03). Conclusions. We delineate the Cepheid PL relation using 111 Cepheids with direct distances from the IRSB analysis. The relations are by construction in agreement with the recent HST parallax distances to Cepheids and slopes are in excellent agreement with the slopes of apparent magnitudes versus period observed in the LMC.
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    Hubble Space Telescope Fine Guidance Sensor Parallaxes For Four Classical Novae
    (2013-04) Harrison, Thomas E.; Bornak, Jilian; McArthur, Barbara E.; Benedict, G. Fritz; McArthur, Barbara E.; Benedict, G. Fritz
    We have used data obtained with the Fine Guidance Sensors on the Hubble Space Telescope to derive precise astrometric parallaxes for four classical novae: V603 Aql, DQ Her, GK Per, and RR Pic. All four objects exceeded the Eddington limit at visual maximum. Re-examination of the original light curve data for V603 Aql and GK Per has led us to conclude that their visual maxima were slightly brighter than commonly assumed. With known distances, we examine the various maximum magnitude-rate of decline relationships that have been established for classical novae. We find that these four objects show a similar level of scatter about these relationships as seen in larger samples of novae whose distances were determined using indirect techniques. We also examine the nebular expansion parallax method and find that it fails for three of the four objects. In each case it was possible to find an explanation for the failure of that technique to give precise distance estimates. DQ Her appears to suffer from an anomalously high extinction when compared to field stars on its sight line. We suggest that this is likely due to local material, which may also be the source of the IRAS detections of this object.