arXiv subjects

Kevin Krisciunas

Publications and source records attributed to Kevin Krisciunas.

83 records · Page 5Linked to original sources

arXiv2000

Uniformity of V minus Near Infrared Color Evolution of Type Ia Supernovae, and Implications for Host Galaxy Extinction Determination

From an analysis of SNe 1972E, 1980N, 1981B, 1981D, 1983R, 1998bu, 1999cl, and 1999cp we find that the intrinsic V-K colors of Type Ia SNe with multi-color light curve shape (MLCS) parameter -0.4 < Delta < +0.2 suggest a uniform color curve. V-K colors become bluer linearly with time from roughly one week before B-band maximum until one week after maximum, after which they redden linearly until four weeks after maximum. V-H colors exhibit very similar color evolution. V-J colors exhibit slightly more complex evolution, with greater scatter. The existence of V minus near infrared color relations allows the construction of near infrared light curve templates that are an improvement on those of Elias et al. (1985). We provide optical BVRI and infrared JHK photometry of the Type Ia supernovae 1999aa, 1999cl, and 1999cp. SN 1999aa is an overluminous "slow decliner" (with Delta = -0.47 mag). SN 1999cp is a moderately bright SN unreddened in its host. SN 1999cl is extremely reddened in its host. The V minus near infrared colors of SN 1999cl yield A_V = 2.01 +/- 0.11 mag. This leads to a distance for its host galaxy (M 88) in agreement with other distance measurements for members of the Virgo cluster.

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arXiv1999

Observatories

I give a brief history of astronomical observatories as an institution. This includes: 1) observatories in Islam; 2) China and India; 3) early European observatories; 4) the rise of national observatories; 5) private (amateur) observatories; 6) mountaintop observatories and the modern era. Additional references, to material not cited in the version that will be published in the encyclopedia, are also given.

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arXiv1998

The Recognition of Unusual Objects in the Sloan Digital Sky Survey Color System

We present 5 filter photometry of 21 carbon stars, 15 asteroids, 15 cataclysmic variables, 6 metal-poor stars, 5 Cepheids, 1775 field stars, blue horizontal branch (BHB) stars and RR Lyrae stars in the globular clusters M 15 and M 2, two primary standards, and 19 secondary standards. The photometry was carried out using a filter set identical to that which will be used for the Sloan Digital Sky Survey. We find that carbon stars, CVs, R-type, J-type, and V-type asteroids, BHB stars, and RR Lyr stars should be identifiable on the basis of SDSS photometry alone, while Cepheids, metal-poor stars, and many types of asteroids are indistinguishable from the stellar locus of field stars.

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arXiv1995

New Photometry of the Hyades $δ$ Scuti star V777 Tau (71 Tau)

71 Tau was discovered to be a $δ$ Scuti star by Horan (1979, AJ 84, 1770). To our knowledge no other photometry of this star has been published. 71 Tau is the second brightest X-ray source in the Hyades and has been shown to be variable by as much as 30 \% at ultraviolet wavelengths near 1700 to 2000 Å. We find that the best two-frequency fit to the new photometry is obtained with $f_{1}$ = 5.485 and $f_{2}$ = 7.637 d$^{-1}$, with amplitudes $A_{1}$ = 6.0 and $A_{2}$ = 3.4 mmag, respectively. However, one-day aliases of these frequencies {\em could} be the true values. (For $δ$ Scuti stars pulsating radially the ratio of first overtone period to fundamental period is 0.773.) It would be useful to obtain more extensive data runs on this and other $δ$ Scuti stars in the Hyades.

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arXiv1995

Mode Identification of the Slowly Pulsating F0V Star V398 Aurigae (9 Aur)

We have investigated the F0V star V398\,Aurigae (= 9 Aur) under the assumption that it is undergoing non-radial gravity mode oscillations and that the two principal periods given by Krisciunas et al. (1995) are correct. We find that the two periods are manifestations of an $\ell=3, |m|=1$ spheroidal mode and its toroidal corrections due to the rotation of the star. As far as we know, this is the first detection of toroidal correction terms in a real star. The two modes probably are the result of rotational splitting. Our analysis provides for the first time a physical explanation of certain characteristics of the observed behavior of the star. The amplitude of the radial part of the pulsation for $f_1 = 0.795$\,d$^{-1}$ is a factor of 4 larger than the one for $f_2 = 0.346$\,d$^{-1}$. Since the photometric variability is determined mostly by temperature variations, which in turn are determined by the radial part of the pulsation, the photometric variability is dominated by the mode with frequency $f_1$. On the other hand, $f_2$ is the more pronounced one in all three spectroscopic moment variations (including the radial velocity), reflecting that the transverse displacement of $f_2$, and not the one of $f_1$, dominates the velocity behavior.

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arXiv1995

A Search for $γ$ Doradus-Type Variable Stars in the Hyades

$γ$ Doradus stars are photometrically variable early F-type stars on or just above the main sequence in the Hertzsprung-Russell Diagram. They vary by as much as 0.1 mag on time scales an order of magnitude slower than the fundamental radial pulsation period. These brightness variations are presumably due to non-radial gravity-mode pulsations. We obtained high precision $V$-band photometry of 8 F0 to F5 stars in the Hyades (BS 1319, BS 1354, BS 1385, BS 1408, BS 1430, BS 1432, BS 1459, and BS 1472) and found that none of them showed strong evidence of $γ$ Dor-type variability. Since $γ$ Dor-type candidates are found in the Pleiades and in NGC 2516 (having ages of 78 and 137 Myr, repectively) but apparently not in the Hyades (age $>$ 600 Myr), we hypothesize that the $γ$ Dor phenomenon is a characteristic of relatively young F stars. Two of the stars investigated showed marginal evidence of low-amplitude variability. The $\pm$3 mmag variability of the F5 star BS 1319 is most likely due to rotational modulation of star spots, though it is not impossible that it is a $γ$ Dor star. Another F5 star BS 1459 ($ΔV = \pm 2$ mmag) has a possible period similar to $δ$ Scuti stars, but no firm conclusions should be made concerning its behavior unless and until its variability is confirmed.

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arXiv1994

9 Aurigae: Strong Evidence for Non-Radial Pulsations

We present further photometric observations of the unusual F0 V star 9 Aurigae and present evidence that this star's radial velocity, spectroscopic line widths and line depths are also variable with the same frequencies as the photometric data ($f_1 \approx 0.795$ and $f_2 \approx 0.345$ d$^{-1}$). The phases of these sinusoids are stable over time scales of longer than one year, though the amplitudes can vary, making the prediction of photometric behavior impossible. Given that a variety of other explanations have already been discounted (e.g. interactions with a close companion, the existence of a lumpy, orbiting ring of dust, or star spots) and that these variations occur on time scales an order of magnitude slower than the fundamental radial pulsation period, we have very strong evidence that 9 Aurigae exhibits non-radial {\it g}-mode pulsations. Since the power spectrum of the radial velocity data shows frequency $f_2$ but does not clearly show $f_1$, the present data suggest that $f_2$ is associated with a low degree spherical harmonic ($\ell$ = 1 or 2), while $f_1$ is associated with a higher degree harmonic. 9 Aurigae, along with such stars as $γ$ Doradus, HD 224638, HD 224945, and HD 164615, appear to constitute a new class of pulsating variables. These stars are to be found at or beyond the cool edge of the Cepheid instability strip in the HR Diagram. Prior to this, only much hotter stars have been shown to exhibit non-radial {\it g}-modes.

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arXiv1993

Errata in \em {Enclyclopedia of Cosmology}

I have noted a number of errors, most of them quite minor, in the {\em Encyclopedia of Cosmology} (New York and London: Garland), 1993, Norriss S. Hetherington, ed. The majority occur in my mathematically verbose article, ``Fundamental cosmological parameters". Some errata were passed on to me by Prof. Ralph Alpher. In the interests of accuracy, I feel that the corrections should be publicized, since no book review will mention more than a couple of them. Also, the incorrectly typeset equations could lead to serious confusion in the minds of readers seeing such material for the first time.

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arXiv1993

The Sign of Four: A new class of cool non-radially pulsating stars?

In this paper we discuss four early F-type variable stars whose periods are an order of magnitude slower than known pulsators of comparable luminosity. They cannot be stars undergoing simple radial pulsations. For one or more of these stars we can discount the possibility that the variability is due to rotational modulation of star spots, interactions with (or tidal distortions by) a close companion, or obscuration by a rotating lumpy ring of dust orbiting the star. They are certainly not eclipsing binaries. The only possibility left seems to be non-radial pulsations, though this explanation involves difficulties of its own. If they are indeed pulsating stars exhibiting non- radial gravity modes, they would be the first stars on the cool side of the Cepheid instability strip in the Hertzsprung-Russell Diagram to be so identified.

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arXiv1993

Look Back Time, the Age of the Universe, and the Case for a Positive Cosmological Constant

We present explicit expressions for the calculation of cosmological look back time, for zero cosmological constant and arbitrary density parameter $Ω$, which, in the limit as redshift becomes infinite, give the age of the universe. The case for non-zero cosmological constant is most easily solved via numerical integration. The most distant objects presently known (approaching redshift z = 5) have implied ages of $\approx$ 1-2 Gyr after the the Big Bang. The range of such age is narrow, in spite of a variety of cosmological models one might choose. We give a graphical representation of a variety of cosmological models and show that a wide range of Hubble constants and values of the age and density of the universe compatible with modern studies are consistent with adoption of a positive cosmological constant.

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arXiv1993

Strange Cases from the Files of Astronomical Sociology

What astronomer could not use his own surname because his father was beheaded for sorcery? Who built the only observatory worth $5 billion in today's money? Who had worse luck than YOU travelling thousands of miles NOT to observe an astronomical event? Who had one of his books bound in human skin at the request of his most ardent fan? Is there an anti-correlation between scientific output and the number of children one has? Are astronomers known for having unusual honeymoons? Who wrote the most egotistical work in the history of astronomy? What famous astronomer was present for the opening of King Tutankhamen's tomb and later began having hallucinations of an elf, which advised him on the running of his observatory? What is the strangest abstract published in the Bulletin of the American Astronomical Society? What well-known bad tempered astronomer was born in 1898 (the year after Bram Stoker's {\em Dracula} was published) in Varna, Bulgaria, which all vampirologists recognize as the nearest port from which any self-respecting Transylvanian vampire would embark on a sea voyage to London? In this article we provide answers to these fascinating questions.

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