The Death of Vulcan: NEID Reveals That the Planet Candidate Orbiting HD 26965 Is Stellar Activity

We revisit the long-studied radial velocity (RV) target HD 26965 using recent observations from the NASA-NSF “NEID” precision Doppler facility. Leveraging a suite of classical activity indicators, combined with line-by-line RV analyses, we demonstrate that the claimed 45-day signal previously identified as a planet candidate is most likely an activity-induced signal. Correlating the bulk (spectrally averaged) RV with canonical line activity indicators confirms a multiday “lag” between the observed activity indicator time series and the measured RV. When accounting for this lag, we show that much of the observed RV signal can be removed by a linear detrending of the data. Investigating activity at the line-by-line level, we find a depth-dependent correlation between individual line RVs and the bulk RVs, further indicative of periodic suppression of convective blueshift causing the observed RV variability, rather than an orbiting planet. We conclude that the combined evidence of the activity correlations and depth dependence is consistent with an RV signature dominated by a rotationally modulated activity signal at a period of ∼42 days. We hypothesize that this activity signature is due to a combination of spots and convective blueshift suppression. The tools applied in our analysis are broadly applicable to other stars and could help paint a more comprehensive picture of the manifestations of stellar activity in future Doppler RV surveys.


Loading
Load with \usepackage[options]{natbib}.See list of options at the end.

Replacement bibliography styles
I provide three new .bstfiles to replace the standard L A T E X numerical ones: plainnat.bstabbrvnat.bstunsrtnat.bst

Basic commands
The natbib package has two basic citation commands, \citet and \citep for textual and parenthetical citations, respectively.There also exist the starred versions \citet* and \citep* that print the full author list, and not just the abbreviated one.All of these may take one or two optional arguments to add some text before and after the citation.et al., 1990;James et al. 1991) \citep{jon90,jon91} ⇒ (Jones et al., 1990, 1991) \citep{jon90a,jon90b} ⇒ (Jones et al., 1990a,b)

Numerical mode
These examples are for author-year citation mode.In numerical mode, the results are different.

Forcing upper cased names
If the first author's name contains a von part, such as "della Robbia", then \citet{dRob98} produces "della Robbia (1998)", even at the beginning of a sentence.One can force the first letter to be in upper case with the command \Citet instead.Other upper case commands also exist.
These commands also exist in starred versions for full author names.

Citation aliasing
Sometimes one wants to refer to a reference with a special designation, rather than by the authors, i.e. as Paper I, Paper II.Such aliases can be defined and used, textual and/or parenthetical with: ⇒ (Paper I) These citation commands function much like \citet and \citep: they may take multiple keys in the argument, may contain notes, and are marked as hyperlinks.

Selecting citation style and punctuation
Use the command \bibpunct with one optional and 6 mandatory arguments: 1. the opening bracket symbol, default = ( 2. the closing bracket symbol, default = ) 3. the punctuation between multiple citations, default = ; 4. the letter 'n' for numerical style, or 's' for numerical superscript style, any other letter for author-year, default = author-year; 5. the punctuation that comes between the author names and the year 6. the punctuation that comes between years or numbers when common author lists are suppressed (default = ,); The optional argument is the character preceding a post-note, default is a comma plus space.In redefining this character, one must include a space if one is wanted.

Other formatting options
Redefine \bibsection to the desired sectioning command for introducing the list of references.This is normally \section* or \chapter*.
Define \bibpreamble to be any text that is to be printed after the heading but before the actual list of references.
Define \bibfont to be a font declaration, e.g.\small to apply to the list of references.
Define \citenumfont to be a font declaration or command like \itshape or \textit.
Redefine \bibnumfmt as a command with an argument to format the numbers in the list of references.The default definition is [#1].
The indentation after the first line of each reference is given by \bibhang; change this with the \setlength command.
The vertical spacing between references is set by \bibsep; change this with the \setlength command.

Automatic indexing of citations
If one wishes to have the citations entered in the .idxindexing file, it is only necessary to issue \citeindextrue at any point in the document.All following \cite commands, of all variations, then insert the corresponding entry to that file.With \citeindexfalse, these entries will no longer be made.

Use with chapterbib package
The natbib package is compatible with the chapterbib package which makes it possible to have several bibliographies in one document.
The package makes use of the \include command, and each \included file has its own bibliography.
The order in which the chapterbib and natbib packages are loaded is unimportant.
The chapterbib package provides an option sectionbib that puts the bibliography in a \section* instead of \chapter*, something that makes sense if there is a bibliography in each chapter.This option will not work when natbib is also loaded; instead, add the option to natbib.
Every \included file must contain its own \bibliography command where the bibliography is to appear.The database files listed as arguments to this command can be different in each file, of course.However, what is not so obvious, is that each file must also contain a \bibliographystyle command, preferably with the same style argument.

Sorting and compressing citations
Do not use the cite package with natbib; rather use one of the options sort or sort&compress.
These also work with author-year citations, making multiple citations appear in their order in the reference list.

Long author list on first citation
Use option longnamesfirst to have first citation automatically give the full list of authors.Suppress this for certain citations with \shortcites{key-list }, given before the first citation.

Local configuration
Any local recoding or definitions can be put in natbib.cfgwhich is read in after the main package file.
Options that can be added to \usepackage round (default) for round parentheses; square for square brackets; curly for curly braces; angle for angle brackets; colon (default) to separate multiple citations with colons; comma to use commas as separaters; authoryear (default) for author-year citations; numbers for numerical citations; super for superscripted numerical citations, as in Nature; sort orders multiple citations into the sequence in which they appear in the list of references; sort&compress as sort but in addition multiple numerical citations are compressed if possible (as 3-6, 15); longnamesfirst makes the first citation of any reference the equivalent of the starred variant (full author list) and subsequent citations normal (abbreviated list); sectionbib redefines \thebibliography to issue \section* instead of \chapter*; valid only for classes with a \chapter command; to be used with the chapterbib package; nonamebreak keeps all the authors' names in a citation on one line; causes overfull hboxes but helps with some hyperref problems.
As an alternative form of citation, \citealt is the same as \citet but without parentheses.Similarly, \citealp is \citep without parentheses.Multiple references, notes, and the starred variants also exist.