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- ID:
- ivo://CDS.VizieR/J/PAZh/21/509
- Title:
- Identification and coordinates in M5
- Short Name:
- J/PAZh/21/509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate equatorial coordinates have been determined for 143 variable and suspected variable stars in the globular cluster M5=NGC 5904. For 28 stars, identifications with Kustner (1933VeUSB..26....1K) catalogue were found for the first time.
- ID:
- ivo://CDS.VizieR/J/PAZh/23/454
- Title:
- Identification and coordinates in M 53
- Short Name:
- J/PAZh/23/454
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Equatorial coordinates have been determined for 61 variables in the northern globular cluster M 53 and for 12 variables in the southern globular cluster NGC 2808 with accuracy sufficient for reliable identifications. A number of errors have been revealed in publications on variable starts in M 53.
- ID:
- ivo://CDS.VizieR/J/PAZh/20/693
- Title:
- Identification and coordinates in NGC 5272
- Short Name:
- J/PAZh/20/693
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Equatorial coordinates of variable stars in the globular cluster M3 (NGC 5272) and its nearest surroundings, mainly measured on a plate taken with The Zeiss-1000 telescope, are presented. Positions in a homogeneous system are presented for the first time for objects from the Catalogue of variable stars in globular clusters as well as for GCVS and NSV catalogue stars.
- ID:
- ivo://CDS.VizieR/J/other/JHA/47.294
- Title:
- Ilkhanid star table (1232)
- Short Name:
- J/other/JHA/47.2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Ilkhani zij compiled by Nasir al-Din al-Tusi and his colleagues in the first period of the astronomical activities (the 1260s and early 1270s) in the Maragha observatory includes a star table collecting important observations of Islamic astronomers from the early ninth century through the third quarter of the thirteenth century, including the Mumtahan astronomers, Ibn al-A'lam, Ibn Yunus, as well as the Maragha astronomers themselves. This table gives the ecliptical coordinates of 18 bright stars in comparison with Ptolemy's corresponding values. This medieval bright star table is especially interesting for two reasons: first, it provides reliable evidence for the examination of the accuracy of the observations made and the instruments employed (notably, an armillary sphere) in the Maragha observatory. Second, it facilitates a comparative study of the accuracy of stellar observations in medieval Middle Eastern astronomy in the period in question. We have obtained the result that the Maragha astronomers observed more accurate star longitudes than did their predecessors, while for the latitudes, all Islamic observers appear to have gained about the same degree of accuracy. We also discuss two delicate matters raised by this table: first, the problem of the use of the two different values for the rate of precession by the Maragha astronomers in order to convert earlier star longitudes to the epoch of the Ilkhani zij (1{deg}/66 years for Ptolemy's longitudes and 1{deg}/70 years for those measured by their Islamic predecessors); second, the change in the star latitudes essentially related to the various values measured by Ptolemy and the Islamic astronomers represented side-by-side in it. Finally, we briefly discuss a small celestial globe designed by the son of Mu'ayyad al-Din al-'Urdi, the instrument-maker of the Maragha observatory.
- ID:
- ivo://CDS.VizieR/J/ApJ/425/122
- Title:
- IMF from UV stellar photometry
- Short Name:
- J/ApJ/425/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UV stellar photometry is presented for 1563 stars within a 40' circular field in the LMC, excluding the 10'x10' field centered on R136 investigated earlier by Hill et al. (1993). Magnitudes are computed from images obtained by the Ultraviolet Imaging Telescope in bands centered at 1615A and 2558A. Stellar masses and extinctions are estimated for the stars in associations using the evolutionary models of Schaerer et al. (1993), assuming the age is 4Myr and that the local LMC extinction follows the Fitzpatrick (1985) 30 Dor extinction curve. The estimated slope of the initial mass function (IMF) for massive stars (>15M_{sun}_) within the Lucke and Hodge (LH) associations is {gamma}=-1.08+/-0.2. Initial masses and extinctions for stars not within LH associations are estimated assuming that the stellar age is either 4Myr or half the stellar lifetime, whichever is larger. The estimated slope of the IMF for massive stars not within LH associations is {gamma}=-1.74+/-0.3 (assuming continuous star formation), compared with {gamma}=-1.35, and {gamma}=-1.7+/-0.5, obtained for the Galaxy by Salpeter (1955) and Scalo (1986), respectively, and {gamma}=-1.6 obtained for massive stars in the Galaxy by Garmany, Conti, & Chiosi (1982). The shallower slope of the association IMF suggests that not only is the star formation rate higher in associations, but that the local conditions favor the formation of higher mass stars there. We make no corrections for binaries or incompleteness.
- ID:
- ivo://CDS.VizieR/J/MNRAS/445/845
- Title:
- Implications of the Galactic aberration for CRF
- Short Name:
- J/MNRAS/445/845
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During the last few years, much attention has been paid to the astrometric implications of the galactic aberration in proper motions (GA). This effect causes systematic errors in astrometric measurements at a {mu}as level. Some authors consider it so serious that it requires redefinition of the Celestial Reference Frame (CRF). We argue that such attention to the GA is exaggerated too much. It is just a small astrometric correction that must be taken into account during highly accurate astrometric and geodetic data processing. The accuracy of this correction depends on the accuracy of the Galactic rotation parameters and, for most applications, on the accuracy of the rotation matrix between Galactic and equatorial systems. Our analysis has shown that our current knowledge of these two factors is sufficient to compute the correction of the GA with an accuracy better than 10 per cent. The remaining effect at the level of a few tenths {mu}as/yr is negligible nowadays. Another consequence of introducing the GA correction is the necessity to return to classical astrometric modelling of the extragalactic radio source position - derived by very-long-baseline interferometry (VLBI) - by the linear trend model. Changing the current paradigm of the VLBI-derived CRF, based on the assumption of zero motion of radio sources, to classical one leads to bias in the radio source positions of up to several tens of {mu}as for a catalogue at epoch J2000.0.
- ID:
- ivo://CDS.VizieR/J/A+A/548/A16
- Title:
- Improved astrometry bor BE74 stars
- Short Name:
- J/A+A/548/A16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate astrometry is required to reliably cross-match 20th-century catalogues against 21st-century surveys. The present work aims to provide such astrometry for the 625 entries of the Bohannan & Epps (BE74; 1974A&AS...18...47B) catalogue of H{alpha} emission-line stars. BE74 targets have been individually identified in digital images and, in most cases, unambiguously matched to entries in the UCAC4 (I/322) astrometric catalogue.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A104
- Title:
- Improving the open cluster census. I.
- Short Name:
- J/A+A/646/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The census of open clusters in the Milky Way is in a never-before seen state of flux. Recent works have reported hundreds of new open clusters thanks to the incredible astrometric quality of the Gaia satellite, but other works have also reported that many open clusters discovered in the pre Gaia era may be associations. We aim to conduct a comparison of clustering algorithms used to detect open clusters, attempting to statistically quantify their strengths and weaknesses by deriving the sensitivity, specificity, and precision of each as well as their true positive rate against a larger sample. We selected DBSCAN, HDBSCAN, and Gaussian mixture models for further study, owing to their speed and appropriateness for use with Gaia data. We developed a preprocessing pipeline for Gaia data and developed the algorithms further for the specific application to open clusters. We derived detection rates for all 1385 open clusters in the fields in our study as well as more detailed performance statistics for 100 of these open clusters. DBSCAN was sensitive to 50%-62% of the true positive open clusters in our sample, with generally very good specificity and precision. HDBSCAN traded precision for a higher sensitivity of up to 82%, especially across different distances and scales of open clusters. Gaussian mixture models were slow and only sensitive to 33% of open clusters in our sample, which tended to be larger objects. Additionally, we report on 41 new open cluster candidates detected by HDBSCAN, three of which are closer than 500pc. When used with additional post-processing to mitigate its false positives, we have found that HDBSCAN is the most sensitive and effective algorithm for recovering open clusters in Gaia data. Our results suggest that many more new and already reported open clusters have yet to be detected in Gaia data.
- ID:
- ivo://CDS.VizieR/J/AJ/160/268
- Title:
- Infrared photometry of binaries in Orion OB1
- Short Name:
- J/AJ/160/268
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Statistics of low-mass pre-main-sequence binaries in the Orion OB1 association with separations ranging from 0.6" to 20" (220 to 7400au at 370pc) are studied using images from the VISTA Orion mini survey and astrometry from Gaia. The input sample based on the CVSO catalog contains 1137 stars of K and M spectral types (masses between 0.3 and 0.9M{odot}), 1021 of which are considered to be association members. There are 135 physical binary companions to these stars with mass ratios above ~0.13. The average companion fraction is 0.09{+/-}0.01 over 1.2 decades in separation, slightly less than, but still consistent with, the field. We found a difference between the Ori OB1a and OB1b groups, the latter being richer in binaries by a factor of 1.6{+/-}0.3. No overall dependence of the wide- binary frequency on the observed underlying stellar density is found, although in the Ori OB1a off-cloud population, these binaries seem to avoid dense clusters. The multiplicity rates in Ori OB1 and in sparse regions like Taurus differ significantly, hinting that binaries in the field may originate from a mixture of diverse populations.
